The AirGun Guild

General Category => PCP, C02, and Helium Powered Airguns => Topic started by: rsterne on January 07, 2017, 11:09:30 AM

Title: Tale of THREE BRods - .25, .30 and .357 Completed, Page 12 !
Post by: rsterne on January 07, 2017, 11:09:30 AM
I have a couple of other projects to finish up, but I wanted to give you a tease about a new project I am about to start.... I have been collecting the parts for nearly a year.... It all started when Travis at W.A.R. was moving his shop and decided to "clean house" and send me a big box of parts.... When I opened my "surprise package" I was pretty enthused with the contents, and could see a lot of the parts required to build two Bottled Marauders.... I scraped together enough money to buy the remaining parts I didn't plan on making myself, and the results of this collecting of bits and pieces is shown below....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Wood_zps8eiv2h5q.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Wood_zps8eiv2h5q.jpg.html)

Above are the parts for a Traditional rifle, using the beautiful stock that Travis supplied.... He also sent me two main tubes, a drop down, and a ton of other parts, including a bunch of valves, one of which (shown) I modded by moving the seat forward and increasing the ports to 7/32" (0.219").... I purchased two receivers from Crosman (through Lloyd Sikes), along with the Gen 1 MRod trigger group.... Below are the parts for the Tactical version.... I purchased another drop down from Travis, the PRod trigger group through Lloyd, and he graciously supplied me with the AR style Buttstock to help this project along.... The valve is a Cothran Powerhouse, which will be used in one of the builds....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Tactical_zpslexalosh.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Tactical_zpslexalosh.jpg.html)

Below is a photo of the tank options I have available.... At the rear is a 500 cc, 250 bar (3625 psi) tank from England, next a regulated 3000 psi 500 cc from Travis, and in the front another 500 cc 3000 psi, but with an adapter to fit directly to the drop down, so that it can be used unregulated.... Travis also supplied me with an adapter for the Metric 250 bar tank as well....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Tank%20Options_zpsu118i1w5.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Tank%20Options_zpsu118i1w5.jpg.html)

I haven't completely decided on the calibers yet, I have several barrels to choose from.... I have a .25 cal LW Polygonal, a .30 cal TJ's, a .308 PB barrel, and a .357 cal TJ's.... I have obtained some 1/2" ID high-modulas Carbon Fibre tubing with a 0.64" OD.... Sleeving the TJ's liners with that would increase the stiffness to at least equal to a steel barrel with a 5/8" OD (the diameter of my other barrels).... and I have determined that I can bore the front of the MRod receivers out to that size forward of the two 4/40 mounting screws.... which will allow me at least 2 diameters of support for the larger barrel inside the receiver for a very rigid, free-floated barrel installation....

All the parts will be interchangeable.... I plan to end up with two receiver/barrel assemblies, which can mount on either main tube.... One tube will contain my modded MRod valve, with suitable hammer, spring, and SSG.... while the other will contain the Cothran valve, with the optimum parts for that.... and both will have their own drop down, a complete, ready to go, pressure assembly, minus tank.... Any of the three tanks can be used on either main tube.... Onto each main tube, I will be able to attach whichever trigger assembly and stock I wish.... I will be making a rear mount for the AR stock that will contain the SSG, of course....

Anyway, that's what my next major project is.... I hope you enjoy following along as it progresses.... My thanks to Travis, Lloyd, and Don for their assistance and generosity....

Bob
Title: Re: Tale of Two BRods
Post by: Dairyboy on January 07, 2017, 12:00:17 PM
I can't wait to see these get done!
Title: Re: Tale of Two BRods
Post by: Monkeydad1969 on January 07, 2017, 09:40:18 PM
Looking forward to the progress... ;D
Title: Re: Tale of Two BRods
Post by: oldpro on January 07, 2017, 11:32:07 PM
me also. get to it Bob.
Title: Re: Tale of Two BRods
Post by: grumpy on January 08, 2017, 05:56:55 AM
Another looking forward to following along on your new project Sir.

Dave
Title: Re: Tale of Two BRods
Post by: bnowlin on January 08, 2017, 06:29:57 AM
Bob,
I love my polygons on my 22 and 25 MRods I got the long ones from Jim G a long time ago and very accurate. one at 22 and one at 25.   Probably can't compare them with prod. but good luck.
Bobn
Title: Re: Tale of Two BRods
Post by: rsterne on January 08, 2017, 11:06:39 AM
The one barrel I really wanted to try was a 14" twist TJs in .257 cal.... but alas I have none left.... and getting barrels (or scopes) out of the US is nearly impossible any more....  ::) .... The aftermath of 9-11 sure screwed things up for legitimate airgunners....  >:(

Bob
Title: Re: Tale of Two BRods
Post by: bnowlin on January 08, 2017, 01:04:22 PM
I know what you are talking about.  I had to box up a shoebox and send it to NY and the guy had to come over to a UPS store in NY and pick it up and pay duty on it and they almost didn't let it across.  Just because the  guy that day new it was used for air guns.  Go figure.
Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 08, 2017, 01:23:16 PM
Getting stuff into Canada is NOT the problem.... it's getting it OUT of the USA.... Optics and barrels are on the ITAR list, just like Nukes....   :o .... Export permits (last time I checked) are $380 US per shipment.... I heard recently that Canada Customs are now giving their US counterparts a heads-up when anything on the ITAR list shows up in Canada.... even though Importation is legal....  ::) .... I better stop, or I will be dragging my own thread of course....  ;D

Bob
Title: Re: Tale of Two BRods
Post by: bnowlin on January 08, 2017, 01:34:29 PM
IK ttyl good luck
Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 08, 2017, 05:00:48 PM
I got around to measuring the plenum volume in the tubes today.... There is 69 cc between the back of the tank block and the front of the valve.... However, in my drilled out MRod valve there is another 4 cc (even more in the Cothran), and in the tank block, which has large passages, there is about another 8 cc.... so the total is over 80 cc.... That means the plenum is large enough for any .25 cal or for a .30 cal pellet shooter for sure.... and for a .257 cal or .30 cal bullet shooter, or .35 cal pellet shooter it is large enough that it would only take about another 100 psi bump in the setpoint to make up for any lack in plenum volume.... It is, however, on the small side for a .308 or .357 bullet shooter, or anything over about 160 FPE, so for those an unregulated setup would be indicated.... The good news is that the passages through the tank block, and the brass tank adapters, are large enough that without the regulator in between, the entire 500cc tank becomes part of the reservoir, able to keep the pressure up during the shot.... This means the effective reservoir is about 580 cc (35 CI) when unregulated....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 10, 2017, 07:12:21 PM
I worked on the tubes today.... The tubes that Travis sent me are intended for Gen 2 MRod parts.... I have two Gen 2 receivers, but I wanted to be able to interchange the tubes from traditional wood stocked rifle to a tactical setup with pistol grip.... Since that needed a PRod trigger group, and it is the same bolt pattern as the Gen 1 trigger, I had to redrill the tubes to accept the Gen 1 and PRod triggers.... In addition, the transfer port hole in the top of the tube had to be drilled out to 3/8" to accept the larger transfer ports.... Here are the redrilled tubes, with the new holes circled....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Drilled%20Tubes_zpscginj7my.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Drilled%20Tubes_zpscginj7my.jpg.html)

The front two holes on the bottom are drilled and tapped with 8-32 threads, while the rear hole on the bottom is the clearance size for an 8-32 (11/64"), because the rear trigger screw threads into the rear tube plug.... A custom rear plug will be required because the bolt pattern is Gen 1 on the bottom and Gen 2 on the top, to accept the two rear 4-40 screws that hold down the receiver.... The only change on the top was drilling the original TP hole out to 3/8" in the same location....

I installed the male Foster and gauge in the tank blocks (drop downs), along with a 1/4"-NPT flush plug on the bottom.... I want to be able to tether the guns without having to waste all the air to fill the 500 cc bottles during development, so I made a blanking plug for the tank/regulator mount in the drop down from an old regulator bonnet....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Tank%20Block%20and%20Plug_zpsoz964m1a.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Tank%20Block%20and%20Plug_zpsoz964m1a.jpg.html)

I simply removed the pin valve and drilled and tapped the bonnet for a 1/8"-NPT flush plug to seal it.... I installed a couple of 5/8" long 10-32 SHCSs in the threaded holes in the bonnet and screwed them in until they touched each other in the middle.... This gives me something to grip better with my fingers to screw the blanking plug into the front of the tank block.... You can see the O-ring that seals the regulator bonnet to the tank block sitting on the bonnet.... It seals in the recess in the front of the tank block, instead of way down inside, so you don't use an O-ring in the normal location on the bonnet.... Travis is to complimented on this arrangement, it certainly is a lot easier to machine, and less prone to leaks, IMO.... I then installed the valves in the tubes, and threaded in the drop downs, stopping with them pointing downwards, lined up with the trigger group.... Once there is pressure inside, they won't have any tendency to rotate, and it isn't important for them to be screwed up tight against the end of the tube (and it you do, they won't line up with the trigger on the bottom of the tube.... You simply screw them in all the way and then back them out until they line up with the trigger.... I then installed my blanking plug and checked for leaks.... Here is the assembly, which I will leave overnight to make sure it holds pressure....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Assembled%20Tube_zpsjwln6ifp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Assembled%20Tube_zpsjwln6ifp.jpg.html)

For the eagle-eyed amongst you, you will notice that the gauge is showing over 3000 psi.... I filled the tube to 3000 psi exactly with a known gauge, but this one shows 3500.... In fact, it was 500 psi high all the way from the start of the fill.... Does anyone know if that is an MRod gauge?.... Anyway, it's nice to get a start on this project, other than just collecting parts for it....

Bob
Title: Re: Tale of Two BRods
Post by: bnowlin on January 10, 2017, 07:56:32 PM
Bob
It looks like a benji gauge and calibrates easy with known gauge by by squeezing the top of the gauge easily remove the plastic or glass and turn the back plate to correct psi or get one from Travis they are great. You probably already know all that.
Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 10, 2017, 09:00:39 PM
Thanks, I'll try that....  ::)

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on January 10, 2017, 09:28:53 PM
 bob wont drilling the forward hole put the front trigger screw into the high pressure area in front of oring on valve?
Title: Re: Tale of Two BRods
Post by: rsterne on January 11, 2017, 08:26:44 AM
Nope, it's still within the recess in the bottom of the stock (Gen 1) valve, and exactly in the forward screw recess on the Cothran Valve.... Makes sense, the valve location, relative to the Gen 1 trigger was the same, right?....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on January 11, 2017, 10:31:45 AM
Yes sir your correct. just looked far forward from the perspective. Well stop muddling around here and go get those Brods together.
Title: Re: Tale of Two BRods
Post by: rsterne on January 11, 2017, 08:56:24 PM
bknowlin..... Thanks for the tip on squeezing the gauge to get the lense to pop out.... It was easy to recalibrate the gauge once I did that....  8)

I had a leak in one of the 1/4"-NPT plugs in the bottom of a drop down.... Teflon tape (gas fitter's yellow) didn't work, so I cleaned it all up and tried purple Loctite hydraulic/pneumatic sealant, let it dry overnight, and it still had a tiny line of bubbles.... Tonight I took it apart, and found the threads in the drop block weren't that great, probably why it ended up in my box of free parts.... *LOL*.... They look strong enough, just some chips and rough spots.... So I cleaned it thoroughly, coated both sides of the threads with JB Weld (slow), and it's curing overnight.... If that don't fix it, I won't know how to, because the plug will be permanently glued into place....  ::)

The other tube was perfect, no leaks at all, the pressure held overnight with no loss from 3000 psi....  8)

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 12, 2017, 07:46:54 PM
I started working on the receivers today.... On most of my projects I have to make them from scratch, but for this project I started with two .25 cal MRod receivers and bolts.... The first thing to be done was to drill out the transfer port hole to 3/8" OD, the same diameter as the Cothran valve, and the holes I drilled in the tubes to match.... I plan to use a piece of 3/8" OD Teflon rod, drilled as appropriate, for the transfer port.... So, I set one receiver up on my milling attachment on my lathe, using a stop at one end to minimize the setup on the other one, centered off the existing transfer port hole, and drilled it out to 3/8".... I then took it out of the vice on the milling attachment, put the other one in, checked the hole center, and drilled it as well....

I had decided to drill the front of both receivers to 5/8" for about 1-3/8" deep, staying in front of the two 4-40 screw holes, so that the full diameter part of the barrel will be held rigidly in the receiver.... It doesn't do a lot of good to have a 5/8" barrel and then turn it down to 1/2", all it will do is flap around (bend) where the receiver starts.... I planned on using my 4-jaw chuck, holding the back of the receiver, and drilling the front with a 5/8" drill in the tailstock, but I found that the receiver is VERY flexible where it is machined away for the magazine, so much so I was afraid that it would not run true, and if the drill grabbed, it might bend and destroy the receiver, so I needed another plan.... I chucked a piece of 1/2" cold-rolled steel in the chuck, which was a perfect slide fit in the front hole of the stock receiver.... I then mounted the receiver in my milling attachment vice so that the steel rod rotated and slid back and forth freely, so that insured that the chuck was lined up with the barrel hole in the receiver.... I then simply drilled the hole out with a 5/8" drill to a depth of 1.4" to the shoulder of the drill.... The LW barrel is actually 16mm, which is a few thou over 5/8", and it slid perfectly into the drilled hole.... I drilled the other receiver the same way, and it turns out that the CF tubing I have is also 16mm OD, so it also fits nicely into the new, larger hole in the front of the receivers.... Here is what they look like now....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Modded%20Receiver_zpsz7a18rkv.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Modded%20Receiver_zpsz7a18rkv.jpg.html)

I then checked to make sure that the stamped end of the LW barrel was, indeed, the breech, by measuring the land diameter with my new small hole gauges.... I found out that the land diameter at the breech is 0.247" and at the muzzle it is 0.244", so the barrel has a 0.003" choke.... I machined the breech down to 1/2" OD for 1.5" of length, and checked how it fit into the receiver.... With an O-ring against the shoulder of the barrel, sitting against the drilled shoulder in the receiver, the back of the barrel was about 0.010" too far back for the magazine to slide into place, which I left for now.... I then used a chambering reamer I made several years ago for the LW barrel on my Hayabusa, and machined the chamber and leade to the required depth so that the front of the chamber is just ahead of where the front of the barrel port would be located.... I checked what a bullet and pellet looked like chambered to that depth, and was pleased with the results, so carried on with the next step, which was laying out the barrel port....

I carefully measured the location of the port from where the back of the barrel needed to be to fit against the locating hollow in the magazine, added a 0.010" (because I knew I had some extra length available), set the barrel up in my milling attachment, carefully centered it relative to the chuck, and drilled and milled the barrel port and the 3/8" diameter flat for the transfer port to seal against.... The port transitions from a 1/4" diameter at the TP spot face to 3/16" wide by 5/16" long at the bore line, so I actually can use up to a bore size transfer port should it be required.... After the milling, I touched up the port with a small ball in my Dremel, blending the 1/4" round port into the oblong barrel port, within the thickness of the barrel itself.... I then slid the barrel into the receiver, lined up the transfer port spot face with the hole in the receiver, and tried the magazine.... As expected, the barrel needed to be shortened 0.010" for the magazine to slide into place....

The last step on machining the back of the barrel was to machine the internal O-ring groove to seal the bolt.... If anyone else attempts this build, the location of that groove is CRITICAL.... The groove is 0.070" wide to fit the O-ring, and from the back of the TP spot face to the back of the barrel is only 0.125", so there is only 0.055" of material left TOTAL for BOTH sides of the groove.... The force on the O-ring from air pressure, is backwards, so I left more material there, 0.035", which only leaves 0.020" between the front of the O-ring groove and the back of the TP spot face.... and YES they would intersect if you put the groove too far forward in the barrel.... Anyway, knowing that was an issue, I was careful and all went well, the bolt slides nicely through the O-ring, and the barrel now looks like this....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/25%20cal%20LW%20Barrel_zpsvzx97xja.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/25%20cal%20LW%20Barrel_zpsvzx97xja.jpg.html)

I assembled all the parts so far, just so that I could have a look, and take a photo so that you can see the progress, and the proportions....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Sub%20Assembly_zps5srvmbcg.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Sub%20Assembly_zps5srvmbcg.jpg.html)

I'm very pleased with the progress to date, so I guess it's time to make the hammers and rear plug and SSG next....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on January 12, 2017, 08:26:49 PM
Bob now thats it HAMMER TIME might I suggest using MDS Nylon with brass core. You wont believe how well it works in every way. https://www.mcmaster.com/#standard-plastic-rods/=15vz1r8
Title: Re: Tale of Two BRods
Post by: rsterne on January 13, 2017, 08:59:50 AM
McMaster-Carr won't ship to Canada, and I have a hard time believing I will be able to get the kind of power I am desiring with a lightweight hammer.... or are you suggesting just a thin sleeve of Nylon on the outside?.... How does the MDS stand up to the PRod trigger group with the heavy spring that holds the sear up against the hammer?.... It scratches a steel hammer, can't imaging what it might do to Nylon.... I tried replacing that spring with a lighter one, and the sear may not latch consistently, the only downside I have found to the PRod trigger group.... excess hammer drag....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on January 13, 2017, 09:54:57 AM
I use a brass insert in the MDS Nylon hammer and you can have the hardest sear drag imaginable and it wont touch the  MDS Nylon surface the stuff is tough and slick. I dont even use a steel striker on our nylon hammers the thin poppet under all that force wont even dent it.
Title: Re: Tale of Two BRods
Post by: Motorhead on January 13, 2017, 11:46:43 AM
While not using HEAVY springs ... Of the literally 100's of MDS nylon hammers i made & sold these past 5 years or so ... NEVER heard of seen one damaged from the sear contact.
* Beauty of a drop away sear such as the M-rod trigger group is that it has sufficient engagement when cocked and falling away upon firing does not fret or damage it as a SNAG sear does that just hangs onto the corner of hammer and claws away at the corner as it is released  :P 

Bob,
You need a small stick of MDS in 1 1/8" O.D. just let me know and will USPS send you some to fool with.
Just cover the postage ... materials not that costly  ;)
Title: Re: Tale of Two BRods
Post by: oldpro on January 13, 2017, 11:55:53 AM
The Prod has more drag by far but Im telling you its TOUGH!!!
Title: Re: Tale of Two BRods
Post by: rsterne on January 13, 2017, 02:45:15 PM
Thanks for the offer, Scott, I may take you up on it for the Cothran valve.... I think without a metal core it might be too light for my large throated MRod valve.... I'm actually planning a cylindrical steel hammer with a 1" deep x 1/2" bore to allow a longer hammer spring.... I know the stock MRod hammer is milled off on the sides, but I don't know how deep the recess for the spring is.... I plan to start off heavy, I can always make a lighter hammer if needed....

The plan today was to get started on the hammers, but I decided instead to finish off the barrel and receiver.... I marked the locations for the spot faces for the setscrews on the top of the barrel and drilled those.... I installed the bolt and discovered I was missing parts yet again (that's what happens your first time playing with parts from a gun you have never worked on before).... I had to make the small plate that prevents the bolt from over-rotating yet allows the handle to be left or right.... no big deal, just time.... Fortunately I still had some small 2-56 screws left over from my R/C Yacht days to install it.... Once I installed the cocking pin in the bolt I could check the position of the shoulder on the bolt and the length of the probe, and the shoulder was too far forward and the probe too short.... I had heard that the bolt was hardened, so I heated the front cherry red and let it cool slowly, but it was still too hard to drill for a new probe.... I figured it might be just case-hardened, so I ground the tip off the bolt, and sure enough that allowed me to get a bite with a small drill....

Mounting the bolt straight in the lathe chuck was tricky because of the handle and the short mounting surface around that, which is the only place to grab it.... I came up with a neat trick to hold it straight while I tightened the chuck up.... I held the bolt probe in the tailstock Jacob's chuck to hold the end of the bolt centered, ran the handle end into the 3-jaw until the handle touched the chuck face, between two of the jaws, and then tightened the chuck good and tight.... When I undid the tailstock chuck and backed it away and mounted a tiny center drill, it was perfectly centered on the end of the probe where I had ground away the case hardened surface.... I drilled a small center hole, and the changed to a 3/32" drill and drilled in about 3/4".... I then removed the bolt from the chuck and ground the probe off, back to the tapered shoulder, and ground the tapered portion off to get through the case hardening there as well.... Of course since I had previously drilled a hole for the new probe, I had a center hole so that I could use a 60* center in the tailstock and line up the bolt again in the 3-jaw in the headstock.... I checked that it was running straight (it was), and then faced off the shouldered portion of the bolt square.... I checked it for length, and decided I would just put a very slight conical taper on the face from the OD to the probe hole.... This puts the edge of the shoulder flush with the back of the barrel port.... I then used a piece of 3/32" drill shank, glued it into the hole in the bolt, and then cut it to length for the new probe.... I made the probe long enough to seat JSB Kings with the skirt flush with the front of the barrel port.... That puts the King Heavies about 1/16" further forward, because they have a shallower hollow in the base, and a cast bullet would sit with the base 1/8" ahead of the front of the barrel port.... You can see what the probe looks like in the photo below....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/006%201024x336_zpsonxogrvz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/006%201024x336_zpsonxogrvz.jpg.html)

I calculated the remaining area for airflow around the probe, and it works out to the same as a 15/64" transfer port.... I will likely be using a 7/32" port, which is the same size as the exhaust port in my modded Mrod valve (0.219"), so unless I have to go to full area porting should offer no restriction to the flow.... If I do have to use full 1/4" ports, I may have to change to a flat nosed bolt that retracts into a J-slot to allow maximum flow.... but I don't anticipate it, as I'm not trying to build a 100 FPE quarterbore....

At the muzzle I wanted to mount a Hatsan Air Stripper, as I happened to have a spare .25 cal on hand.... This required turning the barrel and threading it 1/2"-20 NF for the stripper.... I found a position in my 3-jaw where the bore ran true, and then faced the muzzle off square to the bore, and then turned the barrel OD down to 0.50" for a length of 0.80" and threaded it.... The photo below shows the installation....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Completed%20Receiver%20and%20Bolt_zpsnesa28ei.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Completed%20Receiver%20and%20Bolt_zpsnesa28ei.jpg.html)

Anyway, I think the upper assembly for the .25 cal version is now complete, and I can get on with the hammer and spring arrangement....

Bob
Title: Re: Tale of Two BRods
Post by: Motorhead on January 13, 2017, 02:59:12 PM
Note ... from memory OEM hammer specs.

O.D. 1.050"
O.A.L. 1.080"
Cocking lug .900" from striker end face
Lug 8-32 threaded ( uses a 8-32 cap screw )
Spring counter bore @ .500" I.D. at .750" deep
Striker hole ( for Adjustable stroke ) threaded 1/4-28 NF
Bevel angle on sear holding front edge * Don't remember & will get you that once home

Title: Re: Tale of Two BRods
Post by: rsterne on January 13, 2017, 03:26:29 PM
Pretty sure the sear angle is 22.5*.... My hammer will be 1.20" LOA because it has no separate striker.... and should be a bit heavier than a stocker.... even with the 1" deep spring recess....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 13, 2017, 06:43:47 PM
I got a chance this afternoon to make the hammers.... I turned them from 1144 Steel.... They are 1.20" long, drilled 0.50" to a depth of 1.00" to the drill shoulder, and weigh 104 grams each.... There is just enough room in the cocking slot to go from contacting the back of the modded valve I made (which was shortened 0.075") to just cocking the trigger, for a total hammer stroke of 0.88" with my valve.... and about 3/4" with the Cothran valve.... With the deeper recess for the spring I have 2.75" of length from the shoulder in the hole to the back of the tube.... This means I can use a 3" spring for my SSG without having to make the rear plug stick out more than 1" behind the tube or so.... I'm pleased with the way they came out....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/104%20gr%20Hammers_zpsrp3eapok.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/104%20gr%20Hammers_zpsrp3eapok.jpg.html)

You may wonder why I am always using heavy hammers with maximum stroke in my builds.... Most of the time I'm going for a lot of FPE with a heavy bullet, and that means I need a large valve throat and lots of dwell.... The hammer energy to crack the valve and create lift comes from the spring and travel, but the hammer momentum to create more dwell comes from hammer weight.... A heavier hammer allows me to use a lighter spring, with a lower cocking force, and still get the FPE I want....

Bob
Title: Re: Tale of Two BRods
Post by: Dairyboy on January 13, 2017, 07:00:32 PM
Can't wait to see what's next!
Title: Re: Tale of Two BRods
Post by: farmerjoe99 on January 13, 2017, 07:43:40 PM
Excellent progress Bob, should be getting your parts any day now.

Have you found the air strippers to help much with accuracy?
Title: Re: Tale of Two BRods
Post by: rsterne on January 13, 2017, 09:29:49 PM
I like them, and I think they have more potential than I have seen as well.... You need a way to make very small, repeatable adjustments.... and the time to experiment, which is where my problem lies.... no time in the summer to truly test....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 14, 2017, 04:57:59 PM
Today I made the first SSG.... I left all the parts longer than necessary until I find out if it will work properly throughout the range of tuning I need, I can always shorten them up and make them prettier later....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/SSG%20Parts_zpsvpm6bkuk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/SSG%20Parts_zpsvpm6bkuk.jpg.html)

The housing is a piece of 1.25" OD 6061-T6 aluminum turned down to fit in the back of the main tube, with the appropriate tapped holes to secure it.... On the top are two 4-40 screws through the receiver on 0.688" centers, and on the bottom a single 8-32 hole that mounts the trigger group.... The front just clears the back of the hammer when it is all the way back.... It is drilled through and tapped 9/16"-18 NF for the gap adjusting bolt.... I know that is huge, but it allows the spring assembly to be withdrawn out the back without any other disassembly.... That is a feature I always like to employ on my RVAs and SSGs, it makes changes a breeze.... The gap adjusting bolt has a spring seat turned on the front end, to hold the spring in alignment.... The stop rod part of the spring guide is a 4.5" long piece of 3/16" drill rod, threaded 10-32 both ends.... At the back it has quite a bit of thread for preload adjustment, which is provided by the two nuts locked against each other.... There is a # 008 O-ring on the shaft to act as a cushion when the guide comes to a halt.... The front part of the guide is turned from a piece of aluminum rod....It is 0.48" OD at the front (the same as the spring) and profiled to fit the bottom of the hole in the hammer.... Behind that is a 1" long section that is 0.355" OD to act as a spring guide.... There is enough space between the two parts of the guide to allow for more preload and cocking distance than I need.... The spring I am using at the moment is 3" long (instead of the 2.5" used in a stock MRod), with a rate of 13 lb/in.... I have 0.40" of preload at the moment, which is about 5 lbs.... If I need more, I just wind the nuts down on the shaft.... If I need less, I can shorten the gap adjusting bolt (moving the rear spring seat back), but a better solution would be a weaker hammer spring.... I just don't have anything lighter at the moment....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/SSG%20Assembly_zpsyozslxl9.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/SSG%20Assembly_zpsyozslxl9.jpg.html)

In the photo above, the SSG is adjusted for zero gap with the current 0.40" of preload with my valve.... With the Cothran valve, where the end of the stem sits further back, the gap adjusting bolt would be further back.... I can shorten the back of the SSG housing to allow more adjustment if I have to increase the preload much.... I'm thinking I'm getting pretty close to being able to tether the version with my valve in it.... That will answer a lot of questions about the hammer spring requirement at various pressures.... The Cothran valve will require less hammer strike than mine, at any given pressure, so I could use a lighter spring, or just increase the gap.... My valve at 3000 psi will be the test of the maximum hammer strike required for these guns....

Bob

Title: Re: Tale of Two BRods
Post by: rsterne on January 15, 2017, 03:58:17 PM
I made the Teflon transfer port today and assembled the gun and fired it for the first time.... Tethered at 1900 psi, at zero gap on the SSG, the velocity was a bit low, so I increased the preload in two 0.10" stages from 0.40" to 0.60", at which point I was able to hit the velocity plateau at zero gap.... I then installed the action in the wooden stock.... It weighs right on 7 lbs. without the bottle....  I haven't done anything with the comb of the stock yet....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/First%20Assembly_zpsgjsuxhzz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/First%20Assembly_zpsgjsuxhzz.jpg.html)

I then tested the velocity with 25.4 gr. JSB Kings and 34.2 gr. JSB Heavies, adjusting the Gap from zero out until the velocity dropped below 600 fps.... and then went the other way, adding preload (negative gap) until the plateau was confirmed.... ie I knew what the maximum possible velocity was with this valve, and 0.219" ports, at 1900 psi.... Here are those results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Tethered%201900_zps63qwn61m.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Tethered%201900_zps63qwn61m.jpg.html)

As expected, adding any preload against the valve stem instantly increased the report.... I like to adjust the preload on my SSGs until I can reach the velocity plateau just as the gap goes to zero.... Any more preload and you are just making the gun harder to cock, and it means that you have to increase the gap to drop the velocity back down to the knee of the curve.... I want just a bit more power, I would like to be on the knee of the curve at about 950 fps with the 34 gr. Heavies, so with this valve I would need to increase the regulator setpoint slightly, I think 2000 psi should be about perfect.... However, before I make that decision, I want to test the other tube with the Cothran valve at the same pressure, to compare the results....

All in all, I'm delighted with the initial results.... With the SSG adjusted so that there is a tiny gap, I am at 944 fps (68 FPE) with the 34.2 gr. JSB Heavies, at only 1900 psi.... Moving the seat forward in the MRod valve so that I was able to achieve the 7/32" exhaust port was worth the effort....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on January 15, 2017, 04:07:39 PM
 That stock came out pretty cool!!!! I like it!!!
Title: Re: Tale of Two BRods
Post by: rsterne on January 15, 2017, 06:18:33 PM
I'm going to add a cheek-piece.... I think a piece of 1-1/4" ABS pipe will be just about the right height, and carry the black back onto the stock.... Until I get some optics mounted I won't know for sure what height to mount it at tho....  Once again, Travis, thank you so much for all the parts.... that stock sealed the deal to kick my butt into doing this project.... so it's all your fault....  ::)

Bob
Title: Re: Tale of Two BRods
Post by: Shorty on January 16, 2017, 01:24:31 PM
Nice work Bob.

What's the barrel length for the 25 ?

Can't wait to see the difference in power level or efficiency between the 2 valve systems. This will be the first heads up comparison of the 2.
Title: Re: Tale of Two BRods
Post by: rsterne on January 16, 2017, 02:14:25 PM
The story of todays post is.... NEVER BE AFRAID TO LEARN SOMETHING NEW.... or at least open your eyes to existing problems....  ::)

I am always careful to make sure that the area between the front of the hammer and the back of the valve can't get pressurized, either from the hammer movement itself, or from an air leak through the valve stem during firing.... If that happens, you can get (in the worst case instance of a leaky valve stem) a machine-gun action where the pressure partially recocks the hammer and fires the gun again.... until the reservoir is empty (yes, I've had that happen).... Travis suggested that I flute my hammers to prevent this, but I double checked, and the sear slot in the bottom of the tube vents into the trigger, and out through the bottom.... However, I haven't been paying enough attention to the BACK of the hammer, where a vacuum can build up and slow the hammer strike.... The only gun I ever vented there, on a suggestion from Scott (Motorhead), was my B-51.... WHY I haven't been looking for this problem in other guns I don't know.... complacency, I guess.... Well, that just bit me.... in spades....

While I was triple checking the space in front of the hammer this morning, I looked at the area behind it.... Yes, there is a rather large cocking slot, with a matching one in the receiver.... but guess what.... There is nowhere for the receiver to vent, other than past the bolt at the ends, in an MRod receiver, with the rear bolt.... I had noticed some large ES values yesterday when I had the SSG backed off with a large gap, and the lightbulb finally went on.... With an SSG (or SSS or TSS), the spring quits pushing the hammer before it gets to the valve stem, and it coasts the last part.... What if there is a vacuum behind the hammer?.... Yup, that will start slowing the hammer down before it gets to the valve.... In addition, that vacuum is unlikely to be 100% consistent, shot to shot, which could increase the ES.... and the more gap you have between the spring and hammer, the worse both might be.... Time to find out....

I set the SSG for 1.5 turns of gap, and shot an 8-shot string.... The average velocity was 811 fps, but the ES was huge, with shots going from 790-834 fps.... definitely not good.... I stripped the back of the gun apart, and machined two slots in the bottom of the rear plug (SSG housing), at about 4:30 and 7:30, in the section that inserts into the tube.... The slots were 3/16" wide and 1/8" deep, and continued back 3/16" behind the rear of the tube.... That is the equivalent area of a 1/4" hole through the rear plug to prevent any vacuum forming behind the hammer on firing.... Here is what you see with the action out of the stock....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Vent%20Slots_zps9frg6jrt.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Vent%20Slots_zps9frg6jrt.jpg.html)

There happens to be a slot in my stock at the location of the vents.... If that isn't the case with a different stock, a different vent design may be necessary.... Anyway, I assembled the back of the gun again, adjusted the SSG gap to the same, 1.5 turns out, and fired a 34 gr. JSB through the Chrony.... Instead of 811 fps, it was 956 fps.... WOW !!!.... Obviously the vacuum behind the hammer was a reality, I had moved up onto the velocity plateau.... I went through the process of documenting the velocity vs gap with the vented rear cap.... On the graph below, the dotted red line is the new data, with the vent.... while the solid red line is yesterday's data, without the vent....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Modded%20Valve%20Tethered_zps2rgf1wzp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Modded%20Valve%20Tethered_zps2rgf1wzp.jpg.html)

There are two important things to notice.... First, it takes a LOT more gap to get to the knee of the curve with the vents.... which means that without them, the vacuum behind the hammer was slowing it dramatically.... Secondly, the slope of the downslope part of the curve is a lot shallower.... It takes more gap to lose the same amount of velocity.... To drop from 944 fps down to 760 fps now takes a 3 turn increase in gap instead of two.... That makes sense, because the bigger the gap, in the unvented setup, the more the vacuum would reduce the hammer velocity.... There is absolutely NO doubt this gun needs the area behind the hammer vented.... 

Since I had dramatically increased the hammer strike at the same settings, I could now do two things.... I could reduce the preload on the spring, making the gun easier to cock.... I reduced the preload to my original 0.40" (which was not enough yesterday, with the vacuum), and shot the data shown by the purple line.... As you can see, the "knee" of the curve still requires 3 turns more gap, even though the preload on the spring is reduced from nearly 8 lbs. to just over 5.... Since the larger gap means the spring is not compressed as far (and starts at less preload as well), the maximum cocking force, when the gun is set just below the plateau, at 944 fps, has dropped from 19 lbs. down to just 15 lbs.... In fact, I could further reduce the preload if I wish, and that would allow me to decrease the gap, and the cocking force, even more....

These vents did one more thing for me.... They increased the available hammer strike to the point that I could now test the gun at 2900 psi.... I checked it with the 34 gr. JSB Heavies, and the results are shown as the black line on the graph above.... This was shot with the preload on the spring still at 0.40", and to get to the plateau I had to set a turn of negative gap (actual preload on the valve stem).... I didn't try it, but I am confident that by going back to the 0.60" preload I could operate at 2900 psi and hit the plateau with a small gap.... In any case, these results proved that this valve is capable of cranking out 90 FPE at 2900 psi with the 34 gr. Heavies.... I didn't have the proper sized 51 gr. BBTs for this barrel, the ones I had were sized to 0.250" (so they were likely leaking a bit in the bore).... but by cranking in some preload I managed to find the plateau for them as well.... I was able to hit 963 fps (105 FPE) at 2900 psi with those bullets.... I have ordered an NOE Mould for the 51 gr. BBTs in 0.253/0.255", and the sizing bushings for them.... so at some point in the future I can experiment with them....

In conclusion, I am extremely glad I vented the area behind the hammer to prevent the vacuum from slowing the hammer.... I am frankly shocked at how much hammer strike was lost because of that vacuum, and the horrible ES that it caused.... You can bet I'm going to have a long, hard look at all my Disco based guns.... There may be more consistency, and easier cocking, lurking amongst any of them....  ::)

Tim, the LW barrel is the standard, 23.8" length they sell....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 16, 2017, 05:00:04 PM
After writing the previous thread, I changed all the parts over to the tube with the Cothran Powerhouse valve in it.... This is the best way to compare it to my modded MRod valve, by tethering it at the same two pressures, 1900 psi and 2900 psi, and using the same pellets.... Here are the results.... The horizontal axis on this graph is the same as the one above for my valve, and I used the same colours for the 34.2 gr. JSB Heavies at the two different pressures.... In both cases, the SSG had the same 0.40" preload, and "Zero" is the point where there is just barely a gap in the SSG setup.... The end of the valve stem in my valve is further forward than that of the Cothran valve, so my setup has 0.88" of maximum hammer stroke, whereas with the Cothran valve it is only 0.79".... but that suits the two valves, because mine needs more hammer energy to open.... This means that the SSG has to be adjusted to a different point (about 1.5 turns further out) with the Cothran valve to end up with zero gap.... but zero on both graphs has the same meaning, minimum gap on the SSG....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%20Valve%20Tethered_zpsqkgeaher.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%20Valve%20Tethered_zpsqkgeaher.jpg.html)

You can see at once the huge difference in the response of the Cothran valve to the gap setting.... Basically this valve is either "ON" or "NOT".... It exhibits the typical "cliff" which we have seen in other tests of the Cothran valve.... The most efficient point to operate the Powerhouse valve is just above the point where it no longer opens properly and consistently.... This may only be a matter of one flat (1/6 turn) on the SSG gap adjuster.... I didn't explore the exact location of that point yet, all I was after was the maximum velocity available at the two test pressures, and the range of SSG gap where the cliff started.... Relative to zero gap, at 2900 psi the cliff was at about 2 turns out, compared to requiring actual preload with my valve.... at 1900 psi, the cliff was at about 4 turns out, fairly similar to where the knee was with my valve.... As expected, with the larger ports, the Cothran valve was able to produce a bit more power than my valve was.... Here are the maximum velocity and energy achieved with the two valves at the two test pressures, with the pellet and bullet tested....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Valve%20Comparison_zps8ljr0fdf.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Valve%20Comparison_zps8ljr0fdf.jpg.html)

The port size on my valve is 0.219".... The Cothran valve has a 0.257" exhaust port, I used a 0.250" transfer port, and the barrel port is equivalent in area, but there is a 3/32" diameter probe in the chamber.... This reduces the effective area to that of a 0.234" port.... so it doesn't hurt my valve, but probably handicaps the performance of the Cothran valve slightly.... However, the only way around that would be to just a probeless bolt with a flat face, that retracts flush with the back of the barrel port in the firing position.... This would require milling a "J-slot" in the MRod receiver for the bolt lockup and cocking pin to retract into.... Since I don't plan on using anything heavier than my 51 gr. BBT, and I can already push that to nearly 1000 fps, I simply don't need to bother making that modification to the receiver.... However, if you wanted to use an even heavier bullet, as you might if you fitted a .257 cal barrel, you would be well advised to take the trouble to use a probeless bolt arrangement to achieve full barrel size porting with the Cothran valve....

Bob
Title: Re: Tale of Two BRods
Post by: Motorhead on January 16, 2017, 08:58:58 PM
 :o ... Air the often overlooked drag contributor to those parts put into motion QUICKLY
Great observation and grasping of this frequently overlooked area.
Title: Re: Tale of Two BRods
Post by: oldpro on January 16, 2017, 10:44:50 PM
That brings me to another thought. If we made the front portion of the hammer diablo or bullet shaped would it travel faster if the weight was the same? Instead of the flat frontal area? Or is the speed and distance traveled too short to take any advantage of the better BC?
Title: Re: Tale of Two BRods
Post by: Motorhead on January 16, 2017, 10:51:41 PM
Would think because we're operating within the "Bore" sort of speak ... with no real air flow around the hammer it's dynamics is nearly pure displacement of frontal and rear air re-positioning and those pressures involved.
Title: Re: Tale of Two BRods
Post by: rsterne on January 17, 2017, 08:21:59 AM
I would agree, Scott.... the air doesn't flow around the hammer because of the tube.... Simple flat sides, like a PRod/Challenger hammer may be the best.... unless you need the weight.... As with most airgun stuff, Lloyd has a spreadsheet for hammer data.... and the hammer velocities at valve impact are quite low.... For the one in my gun, with 2 turns of gap and 0.40" of preload, with the hammer and guide mass, the hammer velocity at impact is only 12.3 fps.... After leaving the guide behind, the hammer energy is 0.54 FPE.... assuming it doesn't lose velocity before hitting the valve stem.... The hammer is only moving the same velocity it would if you dropped it a distance of 28"....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 17, 2017, 05:03:26 PM
I pulled my modded valve out of the tube today and bored out the exhaust port to 0.234", and drilled out the transfer port to that diameter as well.... I inspected the MRod poppet, and it has a nice shiny seat, just indented a few thou.... It is not showing any sign of extruding into the port, as I have seen happen with a 0.281" throat.... The throat in my current valve is 0.266", which I have also used before without issue at 3000 psi.... However, I don't want to go any larger.... Unless you change the poppet material, going larger on the port, or using more than 3000 psi, is just asking for trouble.... The throat (when you subtract the 1/8" stem), the exhaust port, the transfer port, the barrel port and the bore (when you subtract the 3/32" bolt probe) are now all the same area.... I consider this the maximum practical for a modded MRod valve, unless you change the poppet, and no point in doing that unless you also go to a probeless bolt....

The larger ports increased the maximum velocity at 1900 psi by 24 fps, from 956 to 980 fps.... Here is the comparison, before and after enlarging the ports....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20New%20Ports_zpssbgjfoiw.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20New%20Ports_zpssbgjfoiw.jpg.html)

I want the ability to achieve 950 fps on the knee of the curve, and with the 0.219" ports I would have needed to increase the regulator setpoint to 2000 psi.... Now I can use 1900 psi and get there.... I adjusted the gap to 3.5 turns out, and shot the following 10-shot string using the 34.2 gr JSB King Heavies, tethered at 1900 psi....

960
959
956
959
959
957
957
960
955
957

ES = 5 fps = 0.5 %
958 fps average
69.7 FPE average

This achieves my goal with these pellets.... I don't have an efficiency yet, that will have to wait until I install the bottle.... I have not yet decided if I will use my valve, or the Cothran, for the regulated .25 cal, either will work perfectly.... The edge for the Cothran valve over mine is now just 10-20 fps at 1900 psi.... depending on how I adjust the SSG gap.... To adjust the velocity on the Cothran valve, you have to change the pressure, as for best efficiency you need to operate it just above the cliff.... It would make sense to use whichever proved to be the most efficient at the velocity I end up shooting.... That has yet to be determined....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 18, 2017, 01:22:30 PM
I've been hearing all about these MDS Nylon lightweight hammers, and this gun, with the current hammer spring, needed a large gap on the SSG, so it seemed a good candidate to try one.... I made one of identical dimensions to the steel one I had, but used a 3/4" diam. steel core and the rest is MDS.... I simply knurled a piece of 3/4" steel, drilled it for the hammer spring, and then bored out a piece of MDS of the correct length to be a press fit, and pressed them together.... I then machined the MDS to the correct diameter, cut off the excess steel at the front and turned it to length, and drilled and tapped the 8-32 hole for the cocking pin through both, then machined the angle for the sear in the MDS.... The finished weight was 51 grams, almost exactly 50% of the original steel one, which was 104 gr.... I installed it in the tube with my valve in it, and tethered the gun at 1900 psi, to duplicate the test I did yesterday of the 0.234" ports.... I used the same 34.2 gr. JSB Heavy pellets, so the ONLY change was the hammer.... Here are the results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Light%20Hammer_zpsi9l2yiia.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Light%20Hammer_zpsi9l2yiia.jpg.html)

With zero gap, the velocity was already starting to fall below the maximum, at 963 fps.... This is virtually identical to the velocity I got with the heavy hammer at 3 turns of gap.... The velocity at 1 turn out with the light hammer was almost the same as at 4 turns out with the heavy hammer as well.... Therefore, reducing the hammer weight by 50% required a 3 turn decrease in gap to obtain the same velocity.... The hammer spring I am using has a rate of 13 lb/in, and 3 turns of the gap adjuster, which is 18 TPI, is 0.165".... That means that the light hammer requires just over 2 lbs. more force to cock the gun, and 0.165" more hammer travel, to obtain the same results....

Using Lloyd's hammer spreadsheet, I calculated the hammer velocity at the instant it left the SSG, and from that the hammer energy and momentum.... To do that, I had to include the weight of the SSG guide (22 grams) during acceleration, to get the velocity, and then subtract it to get the energy and momentum of the hammers.... Here are the results that produced identical (963 fps) velocity and FPE in the pellet, which is what matters, of course....

104 gr. Hammer

Velocity 11.54 fps
Energy 0.471 ft.lb.
Momentum 0.082 ft.lb/sec
Lock time 10.1 mSec
Cocking Force 14.4 lbs.

51 gr. Hammer

Velocity 17.83 fps
Energy 0.554 ft.lb.
Momentum 0.062 ft.lb/sec
Lock Time 7.1 mSec
Cocking Force 16.6 lbs.

These results are skewed somewhat by the admittedly heavy SSG assembly in this gun.... as it represents a much higher percentage of the weight of the light hammer than the heavy one.... However, in this particular application, that's what I got.... There is no question that this lightweight hammer will work in this gun, with either valve, at 1900 psi with the 34 gr. JSBs, it would just be a matter of tuning it for the velocity you want.... There is also no question that it requires about a 15% increase in cocking force to get the same performance.... I expected an increase, but it's nice to actually put some numbers to it.... Bear in mind, this is a pretty powerful .25 cal, delivering 70 FPE at only 1900 psi....

Although I did not try it at 2900 psi, the results I could expect were pretty obvious.... I was unable to max. the velocity out with the 34 gr. JSBs at that pressure with the heavy hammer and 0.40" of preload on the spring.... I think I could just get there with 0.60" of preload at zero gap, which would put the cocking force at about 19 lbs.... With the light hammer, I'm pretty sure I couldn't come close to maxing the velocity using an SSG, I would have to go to a preloaded spring.... Using heavier bullets at 2900 psi it would be even harder to flow enough air to max. them out, even with the heavy hammer.... Even the Cothran valve had to have the SSG dialed down to zero gap with the heavy hammer, to get to maximum velocity with my 51 gr. BBTs....

My conclusion is that the MDS hammers certainly have their place, and can do wonderful things at moderate power and pressures.... However, when you are trying to extract maximum FPE, particularly with heavy bullets and at high pressure.... a heavy hammer helps you get the hammer strike required without using a spring that make the gun too hard to cock.... The Cothran Powerhouse valve, with its ability to open with a much lighter hammer strike, can certainly make use of lighter hammers, however.... I have done no efficiency testing with either hammer or valve, so can draw no conclusions regarding that at this time....

Bob
Title: Re: Tale of Two BRods
Post by: Rdsail on January 18, 2017, 03:23:47 PM
Very impressive. Do you know what kind of efficiency you are getting?

Back when I built my .25 mrod I was able to do 52g slug at 995fps which was about 115 fpe (if I remember correctly). That was with a modified WAR valve. But it was an air hog so I ended up turning it down to 85-90fpe for 20-25 good shots with a 500cc bottle. The efficiency was never great but that was not the point :) The power peak for me was around 2500-2400 psi

I did end up using a 18-20# spring with a lighter hammer. The biggest issue I found was hammer bounce which I end up fixing thanks to travis's help. The hammer was acting as a piston and creating a large air cushion which increase the hammer bounce significantly. I also ended up putting an oring around the poppet stem to create a seal with the valve housing.

I should have kept it and tried all the new goodies as SSGs



Title: Re: Tale of Two BRods
Post by: rsterne on January 18, 2017, 06:40:22 PM
Seems like most of the 51 gr. bullet shooters in .25 cal peak out at around 115 FPE, depending on the actual pressure used.... I got the same with my .25 cal Disco at 2900 psi, and did 112 in this build at the same pressure with the Cothran valve.... The only way to get a bit more FPE without a longer barrel or more pressure appears to be a heavier bullet.... My Disco pushed to 121 FPE with a 58.8 gr.... By the time you tune it to a usable shot string, your results are typical as well.... I got 5 shots inside 5% at 96 FPE average with my Disco using the stock 135 cc tube....

Bob
Title: Re: Tale of Two BRods
Post by: Rdsail on January 18, 2017, 07:09:18 PM
Interesting about the similar results.  In retrospect I should have gone up to .257 or even .30 but it was an experiment.

My biggest problem with the build was taming the hammer. That is were the cothran valve should help by reducing the hammer energy.

I'll stay tune on your build! By far you give the best detail and scientific notations.
Title: Re: Tale of Two BRods
Post by: rsterne on January 19, 2017, 06:16:27 PM
Today I hooked the gun up to a regulated 500 cc tank so that I could take pressure readings on that tank as I shot some short strings to check the efficiency.... I started with the tube with my valve in it, with the MDS hammer.... I adjusted the SSG to zero gap, shot one 8-shot magazine using the 34.2 gr. JSB Heavies, and recorded the average velocity and the pressure drop.... I then turned the SSG gap adjuster out one turn, repeated, and then did the same thing at 2 turns of gap.... I then changed to the 25.4 gr. Kings, shot another magazine with those, and continued, using the lighter pellets, for 2 more turns.... I then replaced the MDS hammer with the steel one, and starting from 4 turns out (where the starting velocity was the same, 945 fps with the 34 gr.), kept going, repeating the above with the steel hammer.... Then I calculated the FPE/CI based on each pressure drop and the total FPE of each string.... and plotted all the data as below....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2025%20Efficiency_zpsfjxvpogp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2025%20Efficiency_zpsfjxvpogp.jpg.html)

The efficiency is very similar with the steel and MDS hammers.... The gauge I was using to monitor the 500 cc tank had 100 psi increments, so all pressure reading are only within about 10 psi at best, but I feel that the trends above are valid, even if the exact values are not perfect because of the 8 shot strings, which resulted in pressure drops from 120 to 240 psi over the 8 shots.... More accurate numbers would require longer strings..... I also averaged the FPE/CI values at the end of the 34 gr. string and the beginning of the 25 gr. string, because they were pretty close (the heavy pellets were a bit better).... The important numbers, of course, are what the efficiency is at the highest velocities tested (945 fps with the 34 gr. JSBs).... 8 shots used 240 psi with the MDS hammer and 230 psi with the steel hammer, so you can call it a wash (that's as close as I can read the gauge).... That works out to 1.08 - 1.12 FPE/CI at 68 FPE.... and that means I can get about 38 shots per tank from 3000 psi down to the 1850 psi setpoint I was using....

I then swapped tubes, fitting the one with the Cothran valve and the steel hammer.... I had to back the SSG wayyyyyyyyy out to find the cliff, because the last time I used that valve, I was getting a vacuum behind the hammer, which I have since cured.... With the steel hammer, the cliff occurred at just over 8 turns of gap on the SSG, and with the MDS hammer at just over 6 turns.... I followed the same procedure as above, but only using the 34 gr. pellets, with the following results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2025%20Efficiency%20Cothran_zpstpnwm13y.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2025%20Efficiency%20Cothran_zpstpnwm13y.jpg.html)

I did not record the pressure drop, or calculate the efficiency, after the velocity fell off the cliff, as there was no point, you would never operate the gun there.... I did find that the difference between the valve opening properly and intermittently (fast and slow shots mixed) was only one flat (1/6 turn) with the MDS hammer, and then 1 more flat put the velocity in the basement.... With the steel hammer, just 1 flat went from full power over the cliff.... You can see that as you approach the cliff from the high-velocity end, the efficiency rapidly increases, particularly over the last turn.... A couple of turns too much on the SG, and the efficiency is a dreadful 0.45 FPE/CI, with the gun using about 80 psi per shot.... The best efficiency occurs just above the cliff.... For 8 shots, the best I could do was 290 psi drop with the MDS hammer and 310 psi with the steel hammer.... Again, those are close enough that there may not be any real advantage to either hammer.... It works out to 0.88-0.94 FPE/CI, which is significantly less than I got with my modded valve.... That works out to 30-31 shots per tank, compared to 38 with my valve.... Note, however, part of that will very likely be the fact that the velocity with the Cothran valve was greater.... 970 fps (72 FPE) compared to 945 fps (68 FPE) for my valve.... If they were tuned to the same velocity, the difference in efficiency may well disappear.... However, that would require running the Cothran valve at a lower pressure than my valve.... likely around 1700 psi instead of 1850, to drop it down to 68 FPE.... That would increase the headroom (pressure difference between fill pressure and setpoint) from 1150 psi to 1300, which in itself would raise the shot count to 34-35 shots per fill.... If there was any increase in efficiency, it wouldn't take much to get back to the 38 shots from my valve.... In all fairness, I would have to say that the efficiency of the two valves is VERY similar.... so much so that a tiny tweak one way or the other could make either valve come out on top....

There is another variable that will likely effect the ultimate FPE/CI numbers.... For all versions except my valve with the MDS hammer, there was a lot of gap in the SSG.... A better solution would be to fit a weaker hammer spring to reduce the gap.... Small gaps generally make for narrower ES values.... I would use the MDS hammer with the Cothran valve, in addition to a lighter spring.... the valve takes that little to open it.... One other thing that could be tried with the Cothran valve would be to artificially limit the lift of the valve by using a bumper on the back of the valve, and an adjustable, recessed hammer face, like Lloyd was experimenting with.... It seems to me that the Cothran valve, as is, simply releases too much air to be efficient in .25 cal. with pellets.... To get the velocity low enough you have to drop the setpoint pressure down a long ways.... I have a gut feeling that using a higher pressure, say 2000 psi instead of 1700, and then limiting how far the valve can open with a stop, may increase the FPE/CI.... I hope Lloyd continues his experiments with that at some point.... Using my valve, I think bumping the pressure up a bit, back to 1900 psi, or maybe even 2000.... and then operating the valve further down on the knee.... will improve the efficiency of that as well.... and may well buy me a few shots below the setpoint, giving me a similar shot count to what I have now, at my 70 FPE goal....

Bob
Title: Re: Tale of Two BRods
Post by: PakProtector on January 22, 2017, 05:05:58 AM
As much as I hated to move things around, when I built the 3/8" transfer port( OD's )Marauders, I moved the port center line forward .015" just to get a bit more wiggle room between the front side of the o-ring groove, and the back side of the transfer port spot face.
cheers,
Douglas
Title: Re: Tale of Two BRods
Post by: rsterne on January 22, 2017, 08:12:39 AM
Yes, it's extremely tight there.... can be done, but the position of the O-ring groove becomes critical.... If you are working from scratch (valve, tube, and receiver) it's easy to move it ahead.... but one of my valves (the Cothran) was already built, so I had no choice.... unless I wanted to make an offset transfer port like Lloyd did on his first Cothran valve build....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 23, 2017, 06:42:20 PM
Today I moved back the port in the .30 cal barrel that I had to line up with the port in the MRod receiver.... I was able to get everything to line up without having to cut another O-ring groove, shorten the barrel and machine a new chamber, so that saved me a LOT of time.... The new barrel port is 0.22" wide by 0.28" long, so it is the same area as the 1/4" transfer port.... and the new spot face around the port is 3/8" to match the receiver, valve, and the OD of the transfer port.... The barrel was already machined for a Hatsan Air Stripper, so with just the change in port location it was ready to fit with a Carbon Fibre sleeve to stiffen it.... The barrel is a TJ's with a 1/2" OD and I had some high modulus CF tubing of that ID that was 16mm OD, the same as the .25 cal LW barrel I used, which I had already machined the receivers to fit.... By insetting the CF tube into the receiver, there is no weak area at the front of the receiver for the barrel to bend, and the high-modulus CF the tube is made of is 50% stiffer than normal CF, which puts it at least as stiff as a steel barrel of the same diameter.... Instead of being able to flex the barrel with your hands, once sleeved, it's like a rock....

I sanded the barrel OD and the ID of the tube with 220 grit to give a bit of "tooth" for the adhesive.... I used Loctite 638 (green) which is high-strength, high-viscosity, intended as a retaining compound for slip-fitted parts with a gap of 0.010" or less.... It has a shear strength of 4500 psi once cured, stronger than most epoxies, has a working time of 4 minutes (or less) and a curing time of 24 hours.... Once cured, I will be giving it a post cure in my wife's oven at 175*F for 3 hours to assure full strength.... You MUST assure that the parts slide together nice and easy, if they stick and you have to force them, you may run out of time, because the tighter the fit, the quicker 638 sets to the point you can't move it.... I used two nuts on the threaded muzzle portion, and an O-ring, as a stop for the sleeve, to insure proper placement.... but a few wraps of masking tape will also work just fine.... Make sure you have the CF tube exactly the length you want, and know where you want to position it, before you apply any glue.... Make sure you plug the ends of the barrel and any ports, with wadded up paper towel, etc., to keep the glue out.... Here is what it looks like with the CF tube glued in place....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/30%20cal%20barrel_zpswyvqvkdk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/30%20cal%20barrel_zpswyvqvkdk.jpg.html)

The portion of CF tube in the receiver is about the same length as the steel part where the port is.... I had to drill out the cone of the Hatsan Stripper to 11/32" to have ample clearance for the .30 cal bullets.... This one started out drilled for a .177 cal.... The other job I did today was to change the cocking and lockup pin in the bolt to 10-32 for safety with the extra loads from the .30 cal.... At the same pressure, the force pushing the bolt back is 44% greater than on a .25 cal, and going up from 8-32 to 10-32 increases the shear area by 45%.... In the .30 cal, at 3000 psi, there is 212 lbs. force on the bolt, and although the stock 8-32 should be able to handle that, if you ever fired the gun without having the bolt handle down, that force would accelerate the bolt backwards, with only that 8-32 bolt to stop it before it hits your face.... We have never heard of Crosman having a problem, but the MRod only goes to .25 cal from the factory.... Using a 10-32 gives me the same safety margin with my .30 cal.... Here is a photo of the receiver showing the new pin and the wider slots for it....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/30%20cal%20Receiver_zpstcib1i3w.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/30%20cal%20Receiver_zpstcib1i3w.jpg.html)

The MRod bolt is case hardened, so the first thing I had to do was heat it red hot around the threaded hole for the pin, and from there forward.... By letting it cool slowly, it anneals the steel, making it much easier to machine.... although there is still a bit of a tough skin.... I carefully lined up the 8-32 hole with my lathe chuck, using a long screw in the chuck, and clamped down the bolt.... I then removed the screw from the chuck, and drilled the hole out and tapped it 10-32.... One tap I had was a bit older, and I thought I might break it, as the metal was still hard to thread.... but my other tap, a nice new one, cut the threads no problem.... I then used a 1/2" long 10-32 SHCS, and loctited on a hex nut, tightened hard against the head of the screw.... I turned the nut, and the head of the screw down to 1/4" OD, and shortened the head about 0.025" so that it was just below flush in the receiver when installed.... I had to mill out the cocking slot in the receiver wider as well, along with the cross-slot on the left side (I will only be installing the handle on the right) so that the new, larger locking pin would fit....

The last thing I did today was to grind off the probe and the nose of the bolt, leaving a 1/4" stub about 3/4" long.... I will make a new .30 cal nose with probe that will be slid over the stub and loctited in place to complete the conversion of the receiver to .30 cal....

Bob

Title: Re: Tale of Two BRods
Post by: oldpro on January 23, 2017, 07:23:33 PM
 Super close now!!!! Keep rocking your almost there.
Title: Re: Tale of Two BRods
Post by: rsterne on January 24, 2017, 06:32:20 PM
I finished up the .30 cal Bolt conversion today by increasing the diameter of the forward section.... Now you can clearly see the larger cocking / locking lug....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/30%20cal%20Bolt_zpsmdxtudva.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/30%20cal%20Bolt_zpsmdxtudva.jpg.html)

I ground off the probe, leaving a straight 1/4" diameter shank 3/4" long.... and then made a sleeve to slide over the 1/4" diameter shank from a piece of 5/16" drill rod.... I turned the front part down to form a probe that is 7/64" in diameter, which just fits inside the base of the JSB 45 gr. and 50 gr. pellets.... The flow area remaining around the probe is the equivalent of a 0.280" port, and the ports in the barrel and Cothran valve are only 1/4", so it should not restrict the flow.... I turned down (filed and sanded, actually, in the lathe) the OD so that it would just slide into the chamber of my .30 cal barrel, checked the alignment, and glued it onto the stub of the bolt with Loctite 638 (green) and allowed it to set....

The shoulder on the bolt nose is located so that the outside edge of it is flush with the back of the barrel port.... and the probe will just push the skirt of the JSB pellets past the front of the barrel port.... When you are making a longer, thinner probe, you are limited in the overall length by how far it will withdraw to clear the back of the magazine.... With the hammer and cocking pin in place, I temporarily install the receiver, with the bolt in place, and pull it back as far as the hammer will allow it to go.... and then mark and cut the probe off flush with the back of the magazine notch.... That will still be a bit long, once you install the trigger, the hammer when cocked will sit slightly forward of that point, and you may have to shorten it a bit more.... The problem is, that if you do, it may not push pellets past the longer barrel port, so you may be stuck with having to hold the bolt back to remove the magazine.... On my .25 cal, I am just able to remove the mag. with the gun cocked, I won't know on this one until the final assembly.... Worst case, I don't mind holding the bolt back to remove the mag. if that is the only way to get the pellet past the barrel port....  Like with many conversions, there is often just enough (or not quite enough) room for things like this....

Bob
Title: Re: Tale of Two BRods
Post by: bnowlin on January 24, 2017, 07:49:15 PM
Gosh Bob, great work. You never cease to amaze me.
Bob the other one
Title: Re: Tale of Two BRods
Post by: Motorhead on January 24, 2017, 09:36:05 PM
Bob,
Am I reading that right ? ..... Breech to Probe seal is that of a Close fit between the two having no mechanical seal present ?
Title: Re: Tale of Two BRods
Post by: rsterne on January 25, 2017, 08:10:08 AM
Don't know where you got that?.... The barrel has a conventional O-ring inside it, per usual MRod practice.... same as I did on the .25cal.... The barrel had already been machined for an earlier project and I guess I just forgot to mention the groove....  :-[

Bob
Title: Re: Tale of Two BRods
Post by: Motorhead on January 25, 2017, 08:15:25 AM
Lol ... or just me reading between lines  ???
Title: Re: Tale of Two BRods
Post by: rsterne on January 25, 2017, 06:08:02 PM
I assembled the .30 cal version today, using the tube with the Cothran valve and the MDS hammer, and did some test shots tethered at 1900 psi and also at 2900 psi.... After about 20 shots at 2900 I started to get some blowby, and within 3 shots, it was severe, with a 200 fps velocity drop.... I pulled the gun apart to find this....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Collapsed%20Transfer%20Port_zpsdpiy5f5h.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Collapsed%20Transfer%20Port_zpsdpiy5f5h.jpg.html)

Yep, that's whats left of the Teflon Transfer Port.... Looking at the damage, I think the bottom edge which was thinned out to clear the O-ring in the Cothran valve failed, which let HPA out between the valve and the OD of the port, which then collapsed the port.... Interesting failure, anyway, and the first time I have had a Teflon TP do anything strange.... If there was no O-ring in the Cothran valve, and the TP tube was full thickness to the bottom, I think it would have been fine, as I have used them at much higher FPE and pressure levels.... Anyway, I'll have to come up with a solution, maybe just use PEEK?....

I was quite pleased with the numbers I achieved.... I tested both the 45 gr. and 50 gr. JSB pellets at 1900 psi, and then tested some NOE 67 gr. BBTs and also some Accurate 71 gr. BBTs at both pressures.... Here are the results, with the SSG gap adjusted so that the valve is operating just above the cliff.... NOTE - I EDITED THE TABLE BELOW AFTER MAKING A BRASS TRANSFER PORT - I GUESS THE TEFLON ONE WAS FAILING, BECAUSE I GAINED 50 FPS ON THE 2900 PSI SHOTS....


(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20Cothran2_zpszgoxrpzu.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20Cothran2_zpszgoxrpzu.jpg.html)

These represent some pretty impressive power at those pressures.... I now have to make the same tests on the other tube assembly, with the steel hammer and my modded valve.... I got my new NOE .253 cal 51 gr. BBT mould today, so once I get some cast up I will be able to see what these guns will do with those at 2900 psi.... I also need to try the 41 gr. BBTs as well.... so lots of testing ahead yet....

Bob
Title: Re: Tale of Two BRods
Post by: caniborrowsomeammo on January 25, 2017, 06:22:36 PM
Bob, I turn my transfer ports out of 3/8 acetal stock. Isn't it (acetal) more rigid than teflon?
Title: Re: Tale of Two BRods
Post by: Dairyboy on January 25, 2017, 06:28:14 PM
Bob, I turn my transfer ports out of 3/8 acetal stock. Isn't it (acetal) more rigid than teflon?
Still have yours in my .25 Brod John works great  ;)
Title: Re: Tale of Two BRods
Post by: rsterne on January 25, 2017, 06:40:15 PM
Yep, Delrin (acetal) is tougher than Teflon, but harder, so doesn't crush to seal as easily.... It just has to be more precise for length, and PEEK would be even harder, and more accuracy for length required.... As I said, I have never had an issue with the Teflon before, I think this was due to having to thin out the bottom of the TP because of the O-ring that protrudes into the 3/8" hole in the Cothran valve.... I wish the valve had a simple milled recess, all metal, but it doesn't, so I will figure out a work-around.... I think the O-ring, being resilient, allowed the thin TP wall to flex outwards and rupture.... then the HPA escaped to the OD of the TP and collapsed it.... I may make a brass TP, and seal it at the top with a 1 mm CS Metric O-ring....

Bob
Title: Re: Tale of Two BRods
Post by: Alan on January 26, 2017, 06:17:05 AM
Self-reenforcing acetal (Delrin) is available in about a dozen different mixes (http://what-when-how.com/materialsparts-and-finishes/acetal-plastics). Thus is pays to select Delrin carefully, and not just by its trade name.
Title: Re: Tale of Two BRods
Post by: caniborrowsomeammo on January 26, 2017, 06:55:31 AM
I don't use the O ring as a seal. I cut to over-length then hit ends with mill bit to create a slight curvature to barrel and valve, hand fitting to about a 32nd over-length and compression fitting with the breech to P tube SHCS (to avoid stressing those tiny 4-40's I clamp breech to P tube before torquing them to 10 inch pounds). It seems to give just enough to seal yet not deform port..

As for composition of mix, I don't know :o. I just order mine from Enco (now MSC) and have never seen or noticed a spec of material. ;D
Title: Re: Tale of Two BRods
Post by: oldpro on January 26, 2017, 09:45:41 AM
 I bored down threw that oring gland and got rid of it and now use a compression oring on both sides of the Tport like on the flex as I had nothing but problems with that sealing method but now its golden.
Title: Re: Tale of Two BRods
Post by: rsterne on January 26, 2017, 12:39:55 PM
Mine seems to be holding just fine with the brass port, no leaks.... I ran all the tests again, with more bullet weights, and determined the position of the cliff.... As expected, it is a bit different with pellets than with bullets.... The lighter pellets need 1/2 turn less SSG Gap (ie slightly more hammer energy) to stay above the cliff.... Here are those results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20Cothran%20Plateaus_zpszqybiqnp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20Cothran%20Plateaus_zpszqybiqnp.jpg.html)

It only takes 1 flat (1/6 turn) on the SSG to go from operating properly to being intermittent, and another flat to see the velocity in the basement.... For the velocity tests with the different bullets I adjusted the SSG so that it was solidly on the plateau.... I added the 62 gr. NOE HollowPoints to the testing today, and also I had some .308 cal 80 gr. BBTs from Accurate that I sized down in 2 step) so that I could try them in this barrel.... All the bullets shot today were sized to 0.300".... Here is the expanded table of results at 1900 and 2900 psi with all bullet weights tested....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20Cothran%20Velocities_zpsn0d4v30b.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20Cothran%20Velocities_zpsn0d4v30b.jpg.html)

Note that the Cothran valve pushes bullets faster at 2900 psi than pellets at 1900.... I didn't do any efficiency testing yet, I'm going to test my modded valve first, putting it through the same tests as I did today with the Cothran....

Bob
Title: Re: Tale of Two BRods
Post by: Dairyboy on January 26, 2017, 02:02:02 PM
Coming together nicely  8)
Title: Re: Tale of Two BRods
Post by: rsterne on January 26, 2017, 04:27:19 PM
I started testing my valve today, and got some data at 1900 psi, but when I changed to 2900 the valve started to leak air out the barrel.... I took a bit more data, figuring it would probably be OK, but the leak got worse so I had to degas the gun and pull it apart.... I lapped the seat and poppet and reassembled, and it still leaked.... I put some soapy water in the exhaust port, and it looked like it was bubbling from the right side, where I had plugged the velocity adjuster hole with epoxy when I inserted the larger, longer seat into the valve when I modded it.... I stripped it apart again, cleaned it thoroughly, and put on some penetrating Loctite, the thin green kind that wicks into threads, hoping it would wick into the cracks and seal them.... I will try it out tomorrow, if it still leaks, I may need to make another valve....

I made an interesting discovery down at my bullet trap this afternoon.... It has several sacrificial layers of particle board, backed by a steel plate, and with all the shooting, it had carved a hole through the layers of wood, down to the steel.... I found these two flattened BBT's laying on the floor, just in front of the trap....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BBT%20at%20150%20FPE_zpsbkmjvqpz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BBT%20at%20150%20FPE_zpsbkmjvqpz.jpg.html)

Pretty KEWL, what 150 FPE can do.... *grin*....

Bob
Title: Re: Tale of Two BRods
Post by: Motorhead on January 26, 2017, 05:30:48 PM
Sorta weird that in winter we get SNOW flakes .... Your getting LEAD flakes  :o
Title: Re: Tale of Two BRods
Post by: rsterne on January 26, 2017, 08:26:24 PM
Yep, no two the same !!!

Bob
Title: Re: Tale of Two BRods
Post by: Motorhead on January 26, 2017, 08:36:18 PM
Yep, no two the same !!!

Bob

Great comeback & so true  ;D ;D
Title: Re: Tale of Two BRods
Post by: rsterne on January 27, 2017, 09:09:31 PM
The leak around the insert I made persisted.... so it was time to remake my valve.... I talked to Travis at W.A.R. and he suggested I bore the valve out 1/2" straight through and make a new insert and seal it with O-rings.... Here is what I came up with....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Valve%20insert_zpsdma6cx4q.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Valve%20insert_zpsdma6cx4q.jpg.html)

This is a pretty radical repair job, but it gave me the opportunity to do some neat things.... I made the insert a bit longer, to make room for the front O-ring ahead of the port, and enlarged the exhaust port to 1/4" at a 20* angle (same as the 7/32" port was before).... I drilled the throat out to 9/32" to handle the flow of the larger port, and made a PEEK poppet to handle the loads of the larger seat.... This makes the exhaust port basically the same size as the Cothran valve, and as the transfer and barrel ports....

The details of this mod are pretty much explained in the photo above.... The insert is 1/2" OD, sealed with two # 012, 90D O-rings.... There is another hole in the valve for a 10-32 setscrew, in the same plane as the three valve mounting screws, and a dimple in the top of the insert for that to tighten into.... That holds the insert securely in the valve while you machine the port and the three holes for the valve mounting screws.... They are blind holes in the insert, tapped 1/8" deep, using the threads in the valve as a guide, which requires slightly longer valve screws, as the same screws hold the valve and insert in place against the 3000 psi reservoir pressure.... The poppet is made from PEEK, with the stem from 1/8" drill rod, threaded 5-40 into the PEEK.... The stem is 0.070" longer than stock (for my shortened valve).... in a stock length valve it would be even longer....

I assembled the valve and installed it into the tube and it held pressure beautifully.... I then set about testing the .30 cal setup with this new valve.... I had hoped that the PEEK would make up for the larger throat, and not require more hammer strike, but alas that was not the case.... I had to use significant preload at 2900 psi, and a bit of preload at 1900 with bullets.... At 1900 psi with pellets, I had to use preload to max. out the velocity, but the knee of the curve is right about at zero gap on the SSG.... Here is how the gun responds the hammer preload, using the same pressures and pellets as I did for the Cothran valve above.... 6.8 turns out from max. is "zero" gap for the SSG, so at 7 turns and out the SSG is operating, at less than 7 turns there is preload on the valve stem....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20PEEK%20Tethered_zpscxuwkahb.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20PEEK%20Tethered_zpscxuwkahb.jpg.html)

When the hammer strike was on the plateau, here are the velocities I achieved with the various pellets and bullets at 1900 and 2900 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20PEEK%20Velocities_zpslvdxpccr.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20PEEK%20Velocities_zpslvdxpccr.jpg.html)

Comparing these maximum numbers to the Cothran valve, at 1900 psi there is virtually no difference in fps or FPE.... At 2900 psi, with pellets my valve is almost there with the Cothran, but with bullets I am losing just a bit with the 62-71 gr. bullets and about 10% less FPE with the 80 gr.... I think I may be running out of hammer strike with the heavier bullets, and the difference between the two valves is now insignificant (as you would expect, with equal ports) except for one thing.... My valve is a LOT harder to open, compared to the Cothran.... I'm using a steel hammer that weighs 104 grams, and a lot of preload on the spring, compared to the Cothran, where I'm using an MDS hammer that weighs 51 grams, and lots of gap in the SSG, in fact I could reduce the preload, or fit a lighter spring.... Don's Powerhouse valve sure is EASY to open.... On the other hand, I can tune my valve down onto the knee of the curve, which should make it more efficient.... I think it's time to start trying to work on improving the efficiency of the Cothran valve by making an adjustable lift arrangement so that I can lower the velocity when using the Cothran valve without lowering the pressure....

Bob

Title: Re: Tale of Two BRods
Post by: rsterne on January 28, 2017, 03:50:03 PM
I went back to the tube with the Cothran valve today, looking to experiment with varying the lift at 1900 psi.... First I had to make a hammer with an adjustable striker position.... This is the second MDS Nylon hammer I have made, and this time I decided to make it even lighter, with an aluminum core.... They are pretty simple to make, actually.... I started with a piece of 3/4" aluminum, faced it off and drilled it through with a #3 drill (the tap size for 1/4"-28 threads) and then used a 1/2" end mill to create the spring cavity 3/4" deep.... I then knurled the outside longer than the hammer, but leaving a smooth area I could hold in the lathe chuck.... I bored a piece of MDS to a few thou over 3/4", but about 0.010" smaller than the OD of the knurling, faced both ends square to a length of 1.25", and pressed them together to form this....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/MDS%20Hammer_zpsirubccns.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/MDS%20Hammer_zpsirubccns.jpg.html)

I then turned the OD to finished diameter to slide smoothly in the tube, and holding the stub of aluminum in a collet I drilled and tapped two 8-32 holes, one for the cocking pin and one for a "brake" to prevent the adjusting screw from adjusting itself.... I then faced off the length at the nose, added the taper for the sear, and tapped the nose through to 1/4"-28, ground the cup point off a 1/2" long setscrew, and installed it with the allen key hole on the inside.... I then dropped a 1/8" long piece of 1/8" diam. Delrin in the front hole, against the side of the adjuster, and topped that off with a 1/4" long 8-32 setscrew, tightened against the Delrin, pressing it into the threads of the adjuster.... Now I can adjust the striker from flush 3 turns in either direction, which is greater than the length of the valve stem on the Cothran valve, so I can go from full lift to no lift in (just under) 6 turns.... Here is the finished hammer, which weighs 28.4 grams (exactly 1 oz.)....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Adjustable%20Hammer_zpsgbuurzdm.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Adjustable%20Hammer_zpsgbuurzdm.jpg.html)

I had a small scrap of energy absorbing polymer sheet about 3/32" thick from Lloyd, which he used in his Cothran valve experimenting, and cut a washer from it with a 3/8" hole (for the striker to clear) and the OD a snug fit in the tube, and installed it hard up against the back of the Powerhouse valve as a bumper to stop the hammer and absorb it's energy.... I removed the spring guide from my SSG, so that I could access the lift adjuster from the back with a long 1/8" allen key, and using the same hammer spring as before, reassembled the gun.... I set the preload on the spring to zero (with the striker just touching the valve stem) with the striker set flush with the face of the hammer.... Assuming the hammer hits the bumper, the valve stem will be driven open about 0.108", and at 0.036" travel per turn of the adjuster, that means that 3 turns out (proud of the hammer face), the striker will push the valve fully open, and backed out about 2.5 turns below flush, it won't open the valve at all.... That was the theory, anyways....

I reassembled everything, tethered the gun at 1900 psi, loaded up a mag. with 45 gr. JSBs, and took a shot.... I had no idea if the valve would cycle properly at these settings or not, and smiled as the shot went through the Chrony at 978 fps, exactly the same as the plateau velocity I had before.... I checked the velocity with more spring preload and it stayed the same, as expected, then reduced the preload, no change at 1 turn of gap, a few fps less at 2 turns, but at 3 turns of gap it dropped to 284 fps.... OK, so there is the normal "Cliff" for the Cothran valve.... I set the preload at 1 turn negative (ie 1 turn of gap), and started adjusting the lift by moving the striker in and out.... When I increased the lift (striker extended), the velocity stayed the same, as expected.... Then I started backing it out, below flush, to reduce the lift on the valve, while leaving the valve cycling properly by virtue of having lots of hammer strike.... I was hoping to be able to have much finer control over the velocity, to give me the ability to control the velocity on the Powerhouse valve without having to change the pressure.... Unfortunately, I was disappointed....

As I recessed the striker into the valve, at 1 turn below flush the velocity held steady at 978 fps.... I figured, "OK, this valve doesn't need much lift".... At 2 turns below flush, I got 321 fps.... much like I did when changing the preload a turn, the valve either cycled or it didn't.... At 2.5 turns out, or further, the valve didn't open, exactly as I had hoped, no shot at all occurred.... I tried various combinations with more preload on the spring, to make sure that I had LOTS of hammer strike, and could not get away from that annoying cliff.... If I was just 1/6 turn (one flat on the allen key) more recessed than where the velocity was steady at 978 fps, the velocity was unstable, it could  be anything from under 600 to over 800 fps.... As I recessed it more, the velocity range dropped, but it was still not stable, fluctuating 100 fps or more, shot to shot.... If anything, I think the velocity was more stable with the valve lift greater, and reducing the preload.... I'm pretty frustrated at this point.... Travis suggested I try a heavier valve spring, but I don't have anything suitable, unfortunately.... At this point, I still have no way to reduce the velocity when using a Cothran valve, other than by dropping the pressure....

Bob

Title: Re: Tale of Two BRods
Post by: Motorhead on January 28, 2017, 10:54:32 PM
 ???
Quote
At this point, I still have no way to reduce the velocity when using a Cothran valve, other than by dropping the pressure....

Sizing down transfer passage on a valve operating in the sweet spot above the cliff I'll assume shifts the cliff just scrambling the sweet spot ???
Title: Re: Tale of Two BRods
Post by: rsterne on January 29, 2017, 09:01:24 AM
It reduces the velocity, without really changing the preload required to find the edge of the cliff.... Since the air is still trying to release the same amount of air, the efficiency doesn't really improve either.... I don't think it softens the edge of the cliff any....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 29, 2017, 06:22:14 PM
I took a break from tuning today to work on the Tactical version.... I measured up the length, selected a hole in the adjustment range of the AR style stock that would give me about 14.5" LOP, and then made the new end plug / stock adapter....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/AR%20Stock%20Adapter_zpscvrnbf3x.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/AR%20Stock%20Adapter_zpscvrnbf3x.jpg.html)

As always, I am astounded how long it takes to make a simple part from scratch, designing on the fly.... about 5 hours for this, believe it or not....  ::)

Bob

Title: Re: Tale of Two BRods
Post by: Monkeydad1969 on January 29, 2017, 06:26:05 PM
Looks nice.
Title: Re: Tale of Two BRods
Post by: rsterne on January 30, 2017, 04:46:58 PM
I installed a taller sear from Lloyd in the PRod trigger group today and installed it on one of the tubes.... Since the PRod tube is thinner wall and smaller diameter, the sear would otherwise not project far enough through the Mrod sized tube to catch the hammer.... Once that was done, then I made a foregrip out of a piece of 1-1/4" ABS black plastic pipe.... It is just the right thickness to fit between the tube and the barrel, and I notched it around the receiver.... It fills the entire space between the trigger group and the drop block....

Here is what the Tactical version looks like with the PRod trigger group, the AR style stock, and the tubing foregrip.... I'm quite pleased with how it turned out....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Tactical%20Version_zpsiuwntmwj.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Tactical%20Version_zpsiuwntmwj.jpg.html)

As shown, with the 500 cc bottle (no regulator) it weighs 7 lbs. 3 oz.... I have never shot a Tactical style gun before, and beauty isn't exactly a strong point, IMO.... but the ergonomics are interesting.... I mounted a scope in Medium height rings, and the cheek weld is really solid and the perfect height for me, with the stock mount lined up with the center of the MRod tube.... That's nice, because that is how I made the mount, and it's a lot easier than making an offset one.... I find the high toe of the stock strange, compared to what I am used to, but the toe of the butt sits nicely in the pocket of my shoulder, so it is actually quite comfortable.... I can see the practicality of a Tactical stock, and how you could quickly grow to like it....

Bob
Title: Re: Tale of Two BRods
Post by: Christopher on January 30, 2017, 05:23:51 PM
Have been following closely.

Great work......as usual.

Chris
Title: Re: Tale of Two BRods
Post by: Monkeydad1969 on January 30, 2017, 05:24:02 PM
I can see the practicality of a Tactical stock, and how you could quickly grow to like it....

Bob

Welcome to the true DARKSIDE, Bob...bwahahahahahaaha!

So says the Monkey!
Title: Re: Tale of Two BRods
Post by: rsterne on January 31, 2017, 03:32:07 PM
Today I made the cheekpiece for the wooden stock....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Stock%20Comb_zpsy1qh91wi.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Stock%20Comb_zpsy1qh91wi.jpg.html)

It is made from a piece of 1-1/4" ABS pipe cut in half and mounted on two short pieces of aluminum tubing.... This stock has a full length groove that is 1.25" in diameter to fit the main tube, that goes all the way to the back.... The pieces of aluminum tubing are mounted in that groove with wood screws, and then the plastic pipe is mounted to the tubing brackets with 6-32 low-profile SHCSs.... This places the top of the cheekpiece the thickness of the tubing (1/8") above the top of the main tube, which is identical to the AR style stock on the "Black" version.... I'm really happy with the cheek weld using that height and medium scope rings.... This completes the work on the wooden stock....

Bob
Title: Re: Tale of Two BRods
Post by: spclark on January 31, 2017, 03:36:47 PM
That looks AWESOME!
Title: Re: Tale of Two BRods
Post by: rsterne on January 31, 2017, 07:11:11 PM
After assembling the wood version with the .25 cal barrel and the Cothran valve, I decided to try some of the 41 gr. BBTs that I cast a week ago.... I tried some as cast, and they were a bit tough to load, they were better at 0.254", and at 0.253" you could feel them seat in the chamber, but you didn't have to push very hard.... I will test different diameters for accuracy at a later date, but for now I am using them sized to 0.253" for my Chrony work.... The hammer is the 28 gr. MDS hammer I made with the aluminum core and an adjustable striker.... I tethered the gun at 1900 psi, set the striker flush with the end of the hammer, and set the hammer spring preload to zero, and started testing.... I am still using the same spring, but without the SSG, so that I can adjust the striker through the middle of the spring and rear adjuster bolt....

I checked the velocity first with the 34 gr. JSB King Heavies, and it was 978 fps (73 FPE) as expected at this pressure... The first shots with the BBTs were 918 fps for the 41.7 gr. FN (78 FPE) and 938 fps for the 39.5 gr. HP (77 FPE).... Leaving the striker flush, I backed out the preload a turn with no change, and then 2 turns, and the velocity tanked.... I then turned the preload back in a turn, it was back to normal, and then I backed out the striker 1 turn below flush (recessed into the hammer).... The velocity was normal, so I backed it out another turn, and the gun did not fire.... The hammer is hitting the bumper on the back of the valve, and at this combination of preload and recessed striker, the valve is not opening at all.... I left the striker recessed, and started adding preload to the spring, and by adding a couple of turns I was able to get it to fire weakly.... After some experimenting with different settings, I decided to set the preload 1 turn out from zero (ie a slight gap between the hammer and spring), and to set the striker 1 turn below flush on the face of the hammer.... At this striker setting, the hammer is hitting the bumper when the valve is open about 0.070", and it really won't matter how much preload I add, it won't open further, at least in theory.... I am hoping that when I connect it back up to a bottle so that I can check the efficiency, I will have found an improvement, both from the heavier bullets, and from limiting the valve lift.... which may reduce the dwell slightly....

The experimenting I have done so far with an adjustable striker mirrors what happens with changing the preload.... Basically the valve is either cycling properly, or it isn't and falls off the cliff.... At 1900 psi the velocity with the 34 gr. JSBs is a bit higher than desired at 978 fps.... while these BBTs are a fraction lower than I want.... I would like to see the FN solids at just under 950 fps, and the HPs at just over, for a solid 80 FPE.... I think bumping the pressure to 2000 psi would do the job.... However, to get results I can compare to my previous ones, I will leave the 500 cc bottle regulated at 1850 psi for now.... and connect it back up for some efficiency testing....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on February 01, 2017, 05:45:39 PM
I did some measurements of the efficiency of the .25 cal version with the Cothran valve today.... I tethered the gun to the 500 cc bottle, with it regulated at 1800 psi, the same as I did previously.... I was using the 28 gram MDS hammer with the aluminum core and adjustable striker, and the same spring but without the SSG in place (so that I can adjust the striker), and the energy absorbing polymer (IsoDamp) bumper on the back of the valve.... With this setup the hammer stops when it hits the valve (bumper), and the amount the valve opens is dictated by the position of the striker, relative to the face of the hammer.... If the striker is flush, the valve can open about 0.108".... if the striker protrudes, it can open further (up to the 0.200" limit of the valve stem protrusion).... and if recessed the valve opens less (recessed 3 turns the valve can't open at all, no matter how much hammer spring you use).... With relatively light preloads, the valve quits opening if the striker is recessed about 2 turns into the hammer face.... ie the gun will not fire at all with the striker recessed more than 2 turns....

As I experiment with the adjustable striker, I am coming to some interesting conclusions about the Cothran Powerhouse valve (whether they are correct or not, I don't know).... I think the valve, once opened a small amount, and with enough backpressure in the exhaust port, "blows open".... From actual lift measurements I made on the Disco version, when cycling properly it opens about 0.060"-0.120".... while when it has fallen "off the cliff" it is opening about 0.020" or less.... Normally, a valve opens pretty much in a linear relationship to the hammer strike, the Cothan does not.... The interesting part is, that with the adjustable striker in this gun, I can get the valve to cycle reliably (providing I have enough hammer strike) with the striker recessed into the hammer face 1.5 turns, which in theory means it can only open the valve about 0.050".... Now perhaps the bumper is compressing, and the valve stem is getting pushed a few thou further, but I don't think there is any way it is getting to 0.060".... and yet the measurements I made with the Disco valve (which is identical inside) say that the valve is opening that far or more.... This has led me to the conclusion (unproven) that once the valve opens about 0.030", it blows open to provide twice that much actual lift.... Right or wrong, that is what I THINK is happening....

Like most valves, if you hit them way too hard, they waste air.... In my first tests with the Cothran valve, whacking it hard didn't produce any more power, but I could make the gun use up to 80 psi per shot, with an efficiency of less than 0.50 FPE/CI.... This is usually an indication that the valve is still open after the pellet has left the muzzle.... As you approached the cliff (from the plateau), the efficiency came up to around 0.65 FPE/CI, and then just before you got to the cliff it increased to just under 1.0 FPE/CI, using about 35-40 psi per shot with the 34 gr. JSB King Heavies.... I was curious what would happen to the efficiency using the adjustable striker to restrict how hard you could hit the valve, regardless of the hammer spring preload.... I wasn't disappointed....

If I set the striker so that it protruded 3 turns from the hammer face (the same thickness as the bumper on the back of the valve), then the bumper never came into play, and the valve acted just like it did before.... Whack it too hard, and the efficiency went into the tank.... When I set the striker flush with the hammer face, however, things changed.... In theory, the valve could only be driven open about half way, and that is exactly the way it acted.... That is far enough to deliver maximum velocity, but not enough to drive the valve so far open that it becomes an air hog.... No matter how much preload I used on the hammer spring, I couldn't get the gun to use more than 40 psi per shot.... Compare this to the 80 psi per shot it would use if you really whacked it before, and you realize that what the bumper does is stop the hammer before it opens the valve further than required, even if you use way too much hammer strike.... It's like having a "limiter" on the amount of air the valve can use.... This is obviously a very good thing, as it makes it extremely easy to not use way too much air.... However, 40 psi per shot is still not great for efficiency, it is only about 0.85 FPE/CI with the 34 gr. JSBs.... It was now time to explore what happened when you tuned closer to the "cliff"....

I now had the ability to approach the cliff in two ways.... I could do it by reducing the preload, or by reducing the initial valve opening, or both.... Believe me, I burned through a lot of pellets and bullets, and a tank of air, trying to figure out what was going on, and which worked better.... I tested with the 34.2 gr. JSB King Heavies, the 39.5 gr. NOE HPs, and the 41.7 gr. NOE FN.... Both the BBTs were sized to 0.253".... I determined that I could recess the striker as much as 1.5 turns into the hammer face and still have the valve cycle properly.... I tried various preloads with it set there, and with it set flush (and in between), and determined that all that happened was it took a slightly different amount of preload to reach the cliff, and the psi of air used for an 8-shot magazine didn't really change.... It was how far from the cliff you were that determined how much air you used.... However, I reasoned that the less lift I allowed with the striker (while still having enough to cycle the valve), the less sensitive the preload might be, and the less difference it would make in air usage if you used too much.... In reality, I don't think it mattered much, but I got some pretty decent efficiency numbers while operating in the 71-75 FPE power range....

Something else I discovered is that the BBTs used less air than the pellets.... I don't know if that is because they were tighter in the bore, heavier, and therefore building more backpressure, causing the valve to close faster, or some other effect.... but instead of 320 psi for 8 shots, they only used 280 psi.... and this was when operating up on the plateau, well above the cliff.... Since I was also getting 2-3 more FPE with the BBTs, this put their efficiency at over 1.0 FPE/CI, instead of under with the pellets.... As I backed off on the preload and approached the cliff, the pressure drop for 8 shots dropped to 270 psi for the pellets and 240 psi for the BBTs, while the velocity only fell off 2-3 fps.... There was about a 1/2 turn range of preload over which the change in velocity and air use was slight, making it much easier to tune just above the cliff, but with consistent velocity.... Here are the final results at 1800 psi....

JSB 34.2 gr.... 969 fps.... 71.3 FPE.... 1.00 FPE/CI
BBT 39.5 gr. HP.... 918 fps.... 73.9 FPE.... 1.17 FPE/CI
BBT 41.6 gr. FN.... 898 fps.... 74.7 FPE.... 1.18 FPE/CI

With the BBTs, I was getting a pressure drop on the 500 cc bottle of 240 psi for 8 shots.... With the regulator set at 1800 psi, that should work out to about 5 magazines (40 shots) at 75 FPE per fill (a total of 3000 FPE).... or about 35 shots with the JSBs at 71 FPE.... I am beginning to think that the Cothran valve is better suited to bullets than pellets.... and quite likely the heavier the better.... If I were tuning for the 34 gr. JSBs, I would probably reduce the setpoint to 1700 psi for 70 FPE.... while for the BBTs I would increase it to 2000 psi, where it should be a good, solid 80 FPE gun.... with a low ES and a decent shot count....

One thing for sure, anyone using a Cothran valve in an MRod might like to consider putting a couple of # 118 O-rings inside the tube, right up against the back of the valve (assuming a stock hammer with flanged, adjustable striker).... If you are using a hammer with a flush face, like the new WAR MDS hammer, a single one should prevent you from opening the valve so far that it will waste a ton of air.... If the valve is capable of opening 0.090" or so, it never needs to open more than that, from what I have seen.... The stem protrudes just under 0.200", so with an O-ring being 0.103" thick, and a flat faced hammer, you should never have to worry about opening the valve too far and dumping air after Elvis has left the building.... Playing with the preload to get close to the cliff and optimize the efficiency is all that would be left to do, once you get the pressure set to give the velocity you want with the pellet you are using....

Bob

Title: Re: Tale of Two BRods
Post by: oldpro on February 01, 2017, 06:16:03 PM
   This is exactly what Ive seen also Bob as the bullet weight goes up the efficiency gos up and this can be contributed to the poppet return orifice in the stem. Inside the poppet stem is a sliding metering rod that acts like a valve. Once high pressure air is introduced into said orifice it blows by metering rod and slams it closed thus preventing the back pressure from getting out then the trapped air forces the poppet closed. Now Don never intended the valve to be used in the manner in which we are trying to use it so POWER is what he was after and using a lot of air to get there. So the more back pressure (heavier bullet) you can produce the faster the valve shuts. So what Im doing literally right now is opening up that tiny .015 hole to .030 to introduce more back pressure and with a heavier return spring also I expect(hope) we will see a much more efficient valve for small bores. Don has been working with me every day and and having him on the team is awesome and having Bob answer my silly questions has saved me so much R&D time.  We will get there Im sure of it. 
Title: Re: Tale of Two BRods
Post by: rsterne on February 02, 2017, 01:59:48 PM
OK, I think I am FINALLY beginning to understand how the Cothran valve reacts to different setups and calibers.... I replaced the .25 cal upper with the .30 cal upper today, with NO other changes.... It was still tethered to the 500 cc tank with a regulated output of 1800 psi, and the striker is still set at 1.5 turns below flush on the hammer.... This means it drives the valve open about 0.050", although it may blow open further than that if it wants to.... I initially used the same 2 turns of gap between the spring and the hammer that I started with yesterday, loaded a magazine up with 7 of the JSB 50.2 gr. pellets, and fired a shot across the Chrony.... about 400 fps.... OK, I half expected it would need a harder hammer hit with the larger bore, so I added a turn of preload.... 930 fps.... GREAT, so now I know that there is hardly any difference in how hard you need to hit the valve with a .30 cal compared to a .25 cal.... That is quite different than a conventional valve, which usually requires a significantly harder hammer strike as you increase the caliber, to fill the larger barrel volume....

I topped up the 500 cc tank, leaving my Great White tethered to it with the valve closed, so that I could use the big gauge to read the pressure drop in the 500 cc (same as I have been doing with all these tests), shot a couple of shots to stabilize everything, recorded the pressure, cranked in 8 turns of preload, and shot a 7 shot mag. across the Chrony and recorded the new pressure.... It dropped 380 psi.... Bear in mind that similar tests without the striker recessed showed as much as 80 psi pressure drop per shot, so the recessed striker certainly saves a lot of air if you have wayyyyyyyyy too much hammer strike.... I backed the preload off to 4 turns, the velocity dropped only 3 fps, and the pressure drop for 7 shots was 300 psi.... I then set the preload to zero, still the same velocity and pressure drop, so the gun was acting exactly the same as it did yesterday with the .25 cal barrel on it, at the same settings.... even the same pressure drop, although this was for 7 shots (at 97 FPE) instead of 8 shots (at 71 FPE).... I then backed the preload out another turn (1 turn of gap, now), lost another 2 fps, but the pressure drop was now only 280 psi.... One more turn out (which worked fine with the .25 cal), and I was back down to ~400 fps, so I added 1/2 turn, and the valve was back to cycling solidly and reliably, at 926 fps (96 FPE), with only a 240 psi pressure drop for 7 shots.... This works out to 1.33 FPE/CI, a very respectable efficiency for a .30 cal gun at this power level.... I only needed 1/2 turn more preload in .30 cal than I did in .25 cal....

So to summarize, when set about 1/2 turn of preload above the cliff, so that the valve cycles solidly, reliably, and with low ES (well under 1%), and shooting pellets.... I am getting 8 shots in .25 cal at 71 FPE on 280 psi of air (1.00 FPE/CI).... and 7 shots in .30 cal at 96 FPE on 240 psi of air (1.33 FPE/CI).... In my Disco Double, at the same pressure, in .357 cal, I was getting 128 FPE at 1.53 FPE/CI (78 gr. pellets @ 862 fps).... I think it is pretty clear what is happening here.... The Cothran valve, when cycling properly but operating just above the cliff.... has a relative constant dwell, so providing the barrel is long enough that the valve is closing well before the pellet reaches the muzzle, it is dumping a relatively constant amount of air into the barrel.... Yes, it dumps a bit more into a larger bore, but relative to the bore volume, it is less, which means the valve is closing sooner in the larger caliber, leading to higher efficiency.... This behaviour also explains why we were getting such high FPE/CI numbers in .357 cal but pretty miserable numbers in .25 cal. and the .30 cal is right in between....

This leads me to a pretty obvious conclusion.... The Cothran valve is a way better choice for larger calibers and heavier bullets.... ie for high FPE applications.... However, as we gain a better understanding of it, we can tame it down for use in regulated PCPs as low as .25 cal....

Bob

Title: Re: Tale of Two BRods
Post by: Monkeydad1969 on February 05, 2017, 05:45:52 PM
Hey Bob,

What is the length of those tubes? 

Joe
Title: Re: Tale of Two BRods
Post by: rsterne on February 05, 2017, 06:32:32 PM
Pretty sure they are 11.75".... From the front of the valve to the back of the tank drop block they are just over 4.75".... The back part of the tube was originally drilled like a Gen 2 MRod.... I redrilled it for Gen 1.... so that it would also accept a PRod trigger....

Bob
Title: Re: Tale of Two BRods
Post by: Monkeydad1969 on February 05, 2017, 08:13:54 PM
Thanks.
Title: Re: Tale of Two BRods
Post by: rsterne on February 06, 2017, 10:00:17 PM
Today, after much prompting by Travis, I started modifying my Cothran valve, to try and improve it's efficiency in my .25 cal regulated BRod.... It is important to realize that these changes may not work (in fact are unlikely to work) in an installation that is prone to hammer bounce.... In my gun, I have an energy absorbing bumper made from "Iso-Damp" on the back of the valve, an extremely light MDS hammer of only 28 grams, a recessed striker that only pushes the valve stem about 0.050", and an SSG.... This allowed me to consider removing the small metering rod (counter-piston) which lives inside the valve stem.... There is a debate as to the purpose of that device, but I believe it to be to prevent the valve from re-opening on a second, or subsequent hammer strike, by acting as a "leaky check valve", slowing the HPA that fills the poppet head during the cycling of the valve from dumping back too quickly into the exhaust port.... I have been told that removing it will cause everything from uncontrollable hammer bounce, to various burps or flutters, to extreme air use, to even destruction of the valve itself.... However, since Travis agreed to supply me with any parts I destroyed I decided to remove it.... I tethered the gun at 1900 psi and started testing.... What happened?.... Exactly NOTHING.... Zip.... NADA....

The valve functioned exactly as before, the same velocity, sound, air use, everything.... I was shocked, but it does reinforce my belief that its primary purpose is anti-bounce.... which I have already addressed by a combination of four different methods.... I did notice one thing that changed, if I leaned on the hammer strike by adding preload (instead of gap) to the SSG.... thereby vastly overdriving the hammer.... the velocity DROPPED slightly, accompanied by a high-frequency "flutter".... I don't know how else to describe it.... It sounded like hammer bounce, but much faster.... The strange thing was, it didn't use more air.... As I said, removing the metering rod may not work in many installations, if they have any possibility of hammer bounce.... but in my gun, set up the way it is, it made no difference, when the SSG was adjusted normally, with a bit of gap.... The velocity was stable until you got to the cliff, and then dropped like a stone, same as always....

OK, so the other thing Travis (and others) have tried is drilling out the tiny vent hole in the valve stem.... This hole lives in the exhaust port, and allows the hollow head of the poppet (which is the diameter of the "force reduction" piston attached to the front of the valve) to be at atmospheric pressure between shots.... This "blanks off" the equivalent area of the poppet, drastically reducing the opening force required to crack the valve.... When you fire the gun, the pressure in the exhaust port rises, HPA flows through that hole, through the valve stem (past the metering rod) and pressurizes the inside of the poppet, providing a greatly increased closing force for the valve.... Without this vent, the valve would stay open, and likely vent the entire reservoir.... With it, the valve cycles in a timely manner, allowing lots of air to escape and produce copious amounts of power.... The way Don builds the valve, I would estimate the dwell time at roughly 2 mSec.... and if you have way too much hammer strike, it can be even more.... Limiting the valve lift keeps that more constant, preventing the valve from being a real air-hog, which is why I like that modification....

In stock form, that vent hole is tiny, only about 0.020".... Logic dictates that enlarging it will make the valve close faster, reducing the dwell.... and that should lead to increased efficiency.... The stem is HARD, and Travis warned me not to try drilling it, and I didn't have small enough drills anyways.... so I did like he did, and used a thin pointed diamond burr in my Dremel and "countersunk" the hole, gradually opening it up at the same time.... The smallest diameter, doing it this way, is just at the very inside of the vent hole, and I found I was causing tiny burrs inside the stem, which I had to keep cleaning out with a #31 twist drill (0.120"), turning it by hand.... I did this in case I had to drop the metering rod (0.118" diam.) back in the hole, I didn't want it to get stuck.... Anyway, I used a couple of sewing needles with the points ground off as go-nogo gauges, and when one that was 0.028" would fit through the hole (but one measuring 0.030" wouldn't) I quit grinding.... I chose 0.028" because it has TWICE the area of the original hole.... I have no idea it that is optimum, but I wanted to start smaller than what others had used, which was 1/32" (0.031") or larger.... I left the metering rod out, reassembled the gun, and repeated my testing.... All I can say is WOW !....

First of all, it took a bit more hammer strike to open the valve.... not a lot, but a couple of turns less gap on the SSG.... Secondly, instead of a completely flat plateau, with only a few fps drop just before you got to the cliff, and then nothing.... I actually saw a "knee" on the curve.... It wasn't long, the sensitivity to SSG gap was still there, but compared to stock it was day and night.... Here are my results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%20Valve%20Modded_zpstkjwkdua.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%20Valve%20Modded_zpstkjwkdua.jpg.html)

Note that the blue (stock) and black (no metering rod) lines virtually lie on top of each other.... At 3 turns of gap on the SSG, the velocity is at maximum, at 4 turns, it has only dropped a few fps, and shortly after that the velocity became unstable (400-500 fps ES) and at 5 turns out it was in the basement.... With the larger vent hole, compared to the velocity at zero gap, there was about a 10 fps loss at 1 turn out, and then about another 15 fps in the next turn.... At 2 turns of gap, the velocity was 25 fps below the peak, and the ES was still less than 1%.... At 2.5 turns of gap, the average velocity dropped another 40 fps, to what in a conventional valve would be the middle of the knee, but the ES had increased to about 2%.... At 3 turns of gap, the velocity was down 200 fps, but the shots were all over the place, with an ES of over 5%.... The valve was becoming unstable, although nowhere near as bad as a stock one.... At 4 turns out, the valve was no longer cycling properly, it was in the basement....

I then tethered the gun to my 500 cc bottle, regulated at 1800 psi, for some efficiency testing.... I left the bottle connected to the gauge on my Great White (valve closed) so I could record the pressure drop for a 8-shot mag. and tested each half turn out, starting at zero gap.... At that setting, the velocity was maximum for this pressure, at 968 fps, and the drop 280 psi, for 0.97 FPE/CI.... This was basically the same as I had before, with the 34 gr. JSB Heavies.... At 1 turn out, the velocity was 962 fps (220 psi) and 1.22 FPE/CI.... At 1.5 turns, 951 fps (210 psi) and 1.24 FPE/CI.... and at 2 turns of gag, 943 fps (200 psi) and 1.28 FPE/CI.... This is far better efficiency than I have ever had before with the Cothran valve in my .25 cal BRod.... At 2.5 turns out, the velocity (809 avg.) was becoming unstable, and it was much worse at 3 turns out (701 fps), so I didn't record the efficiency, figuring it was meaningless....

So, what are my conclusions?.... Well, for one thing, if you have cured all chance of hammer bounce, I think you can try removing the metering rod, I don't think it is necessary.... Secondly, doubling the area of the vent hole, by increasing the diameter to 0.028", decreases the dwell at a given hammer strike, and creates the beginning of a knee to the velocity vs preload/gap curve.... It gives you significantly more control of the velocity just above the cliff, and softens the cliff into a usable, although sensitive knee.... While the operating pressure is still by far the dominant factor in the velocity, you can now detune the velocity just a bit, saving air in the process.... I haven't got all the answers, but I think we're on the right track....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on February 07, 2017, 08:21:48 AM
  Excellent work as usual and I'm confident that if you make the hole slightly larger .035-.040 and put the pin back in but upside down with a spring below it you will get to 1.50 efficiency. The rod is in there to fill the area above the poppet  without it the lock time(dwell) increases due to HP air feeding threw a small hole at high speed then spews into a big void slowing and filling the area now with the pin in it fills up all that void and having the spring in there also fills in the area and also the rod doesn't have to move and this adds to lock time. So put pin in upside down with very small spring below holding pin up and your dwell will again be cut in half and your ES and effecincy will both be much better and it will add another 50 FPS of adjustment below the knee.
Title: Re: Tale of Two BRods
Post by: rsterne on February 07, 2017, 08:43:38 AM
I understand why putting the pin back in, and holding it up away from the vent with a small spring, could help by filling some of the volume inside the head of the poppet, allowing it to fill faster through a given size vent hole.... but why would you turn it upside down?.... Surely the small end (which is closer to the vent) would allow the air to enter the cavity faster than if you turned it around?.... JMO....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on February 07, 2017, 08:47:28 AM
The spring holds it well above the hole so no issues there so having big end down fills in more volume.
Title: Re: Tale of Two BRods
Post by: rsterne on February 07, 2017, 10:05:50 AM
Quote
having big end down fills in more volume.

Seriously?....

Have you looked at the idea of using a longer rod to physically limit how far the valve can open?.... You wouldn't want to subject it to a direct hammer hit, but if the valve is "blowing open" as we suspect, you could limit how far with the length of the rod, no?.... A good place to start might be to allow 1/4 of the throat diameter as the maximum, the flow rate peaks at that point, after that all that happens is the dwell gets longer.... That is about 0.084", IIRC....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on February 07, 2017, 10:23:00 AM
 I did look at that but it would require a lot of changes to the valve. Limiting the travel that way would result in valve failure if gun was dry fired or shot at a low fill pressure so for now it works really good having the rod spring loaded and not moving.  In future valve builds were talking about just moving the hole up seems like simple solution.
Title: Re: Tale of Two BRods
Post by: oneshot61 on February 07, 2017, 12:06:08 PM
Ever thought about 2 small holes, another closer towards the poppet for a stepped result while leaving the pin in place?
Title: Re: Tale of Two BRods
Post by: rsterne on February 07, 2017, 01:41:53 PM
That's why I said "You wouldn't want it subject to a direct hammer hit".... ie you need to stop the hammer the way we are doing now, at about 0.050-0.070" of travel.... but have the rod limit the travel at maybe 0.090-0.100".... to keep if from "blowing open" more than that.... just a thought....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on February 07, 2017, 01:52:54 PM
It has to be idiot proof as someone I guarantee you will over extend the striker or try some fancy mod they think will work and destroy the valve. The valve has to remain undamaged by any strike that may occur from hammer or spring settings not everyone is a Bob....Bob.LOL   
Title: Re: Tale of Two BRods
Post by: rsterne on February 07, 2017, 02:23:26 PM
Yes, I agree, if they didn't install a bumper, there would be a problem.... You could install a bumper on the back of the valve?....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on February 07, 2017, 03:59:55 PM
True but for .50 cents I can add a spring and shorten the rod and no worries ever.
Title: Re: Tale of Two BRods
Post by: rsterne on February 07, 2017, 07:37:46 PM
Today I pulled out the Iso-Damp bumper I had, and substituted a #210 90D O-ring.... I did this because ANYONE can find one of those.... I set the striker FLUSH with the end of the hammer, because then you don't need an adjustable hammer, Travis' new MDS hammer with the flat face would work fine.... The hammer I was using was still very light, at only 28 grams, and I was still running the SSG.... I measured the distance the hammer can push the valve stem with the #210 O-ring in place, and even pushing on the hammer very hard, it only pushes the valve stem 0.075".... I think this is right in the sweet spot, the valve opens plenty far enough, but you can't drive it so far that it becomes an air hog.... I haven't tried this at 2900 psi, but at 1900 psi, it is SIMPLE and works GREAT !.... There was NO change in the settings required with the 0.028" vent hole and no metering rod, the performance was identical to with the Iso-Damp....

This afternoon I put the metering rod back, with a small spring under it, as Travis suggested.... I had it small end down, and the spring was from a Crosman 13XX Safety..... It went coil-bind just before the valve stem went flush with the valve, but that is about 0.100" past where the hammer stops.... Basically there was almost no difference compared to running the valve with no rod at all, running tethered at 1900 psi.... The vent hole was still 0.028", and the peak velocity was a about 10 fps lower at zero gap on the SSG, and also at 2 turns of gap.... At 2.5 turns out, the velocity was about the same as with no rod, but the ES was a bit worse.... At 3 turns out, the velocity was actually 13 fps higher than with no rod, and the ES had increased to over 150 fps over 4 shots.... Not only did I not see an increase in the adjustability of the valve between maximum and the cliff, I was seeing greater instability in velocity than without the rod at all.... I was not at all happy with the way it was performing with the metering rod in place, so I took it back out....

For the next tests, I increased the diameter of the vent hole to 0.0345" (ie between 0.034-0.035"), which TRIPLES the area of the original 0.020 hole in the stem.... I did not use the metering rod.... With the gun once again tethered at 1900 psi, I immediately noticed both a drop in velocity, and a decrease in the report.... I tested hammer spring settings from 8 turns of preload, through zero gap on the SSG, to 4 turns of gap, where it fell off the cliff.... Here is the results, plotted on the same graph I posted yesterday....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%20Modded_zpsbh1t0nsv.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%20Modded_zpsbh1t0nsv.jpg.html)

There are a couple of things to note.... Although I didn't bother to plot it, once I added preload to the hammer spring I noticed the same high-frequency "fluttering" sound I heard yesterday, and with the larger vent hole, it was accompanied by a significant DROP in velocity.... The more preload I cranked in, the lower the velocity got, until at 8 turns of preload it was just over 900 fps.... While not a huge loss, there was no way I could get to the nearly 990 fps velocities I was getting with the same ports, at the same pressure, before I started enlarging the vent hole.... I think this is proof positive that enlarging the hole reduces the valve dwell.... I did NOT try removing the O-ring so that I could drive the valve to greater lift, I don't know if that would move the plateau up again.... but I am pretty sure that doing that would burn a lot more air.... Note that the velocity with the 0.035" vent hole actually peaked at 1/2 turn of gap on the SSG, and fell off both sides of that.... This is completely different than the way the Cothran valve was designed to work.... At 2 turns of gap, the ES had increased to over 50 fps, and at 3 turns of gap it was over 100 fps.... At 4 turns the valve had fallen off the cliff, as expected....

I then tethered the gun to my 500 cc bottle, with an 1800 psi regulated output, to check the efficiency.... I only shot two 8-shot strings, one at the maximum velocity setting of 1/2 turn of gap, and the other with 1.5 turns of gap, where the velocity was still stable.... All I was interested in was comparing the efficiency to what I had with the 0.028" vent hole.... At the higher setting, I got an average velocity of 921 fps (64.4 FPE) and an ES of 1.29 FPE/CI.... With 1 turn more gap, that dropped to 908 fps (24 fps ES at 62.6 FPE) at 1.25 FPE/CI.... Basically, I was getting the same efficiency as with the smaller vent hole, but at 5 FPE less power.... not exactly a great trade-off, IMO.... Yes, I could increase the pressure to get the power back, but I really doubt I would see enough of an increase in efficiency to make up for the decreased pressure headroom.... In this gun, in .25 cal, and at these pressures, IMO I have increased the vent hole too much....

Ohhhhhhhhhhhhh Travis.... I need a new poppet.... *LOL*....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on February 07, 2017, 09:06:14 PM
Did you try with the rod upside down with the large vent hole(.035) yet? Every time I ran the  valve with no vent rod and got to the knee it would flutter so I would have to run under the knee. I imagine the valve doesnt work exactly linear with long and short barrels so somewhere in between is the correct ratio. Im testing a long barrel gun tomorrow with various set ups. Good solid data to work with Bob and Ill see how close our tests compare thats what Im looking for consistency across the spectrum. I do see the .035 string has more gradual adjustment but at a cost to FPS. Getting closer every day. Good work their Bud! One more question before I forget what temp are you running your tests at and altitude?
Title: Re: Tale of Two BRods
Post by: rsterne on February 08, 2017, 08:29:57 AM
Actually, when you take into account the much larger ES as you reduce the velocity (which makes anything under 900 fps unusable), the adjustment range was a bit less with the 0.035" vent.... The only time I had "flutter" was with the SSG adjusted with no gap (ie actual preload).... My shop is between 65-72*F and the altitude here is 2500 ft.... cold outside, so the humidity inside is very low....

I would strongly suggest you try the #210 O-ring of 90D, and a flush faced (non-adjustable) hammer.... The 0.075" travel still opens the valve plenty, yet prevents the hammer over-driving it.... The larger CS O-ring stays in place perfectly, and the 90D isn't very "springy" and seems to kill the hammer energy, preventing bounce.... Once you don't have an adjustable striker, you can run an SSG, or other RVA / TSS, without having to worry about running a long allen key down through the middle.... I would also suggest you try the metering rod small end down.... I will see if I can scrape up enough pellets to test it in the 0.035" with the small end up, but pellets are becoming a valuable commodity now, I can't believe how many I have expended during this testing.... it is nearing prohibitive costs.... and of course I have to have them all shipped in....   ::) .... BTW, I assume you noticed that you can see the coils of the spring through the vent hole, I really do think that making the air get through that, and past the metering rod, isn't the optimum situation.... I think having a smaller hole down inside the stem (say 1/16"), and no rod, would be the optimum, PROVIDING you limit the valve travel and have a hammer that doesn't bounce.... I think a 1/32" vent hole (0.031") may be the optimum for all calibers and pressures.... but of course that is far from being proven.... We have no idea how the larger vent will work in a 250 FPE .357 cal bullet shooter yet....

I tried a couple of shots at 2900 psi, and there was not enough hammer strike with the 28 gr. hammer and the SSG as set for 1900 psi (not surprising).... I want to try the 51 gr. and 104 gr. hammers today, with the same SSG, to see if it will shoot at 2900 psi, without any changes to the valve, just more hammer strike.... Wouldn't it be great if that was the case....  8)

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on February 10, 2017, 01:10:56 PM
As Travis requested, I ran another test today, with the 0.035" vent hole and the metering rod in place, upside down, with the small spring under it.... The rest was unchanged from the previous tests, I was using a single #210 90D O-ring as a bumper, with a flush front on the 28 gr. hammer, and the SSG.... The gun was the .25 cal. version, shooting 34.2 gr. JSB King Heavies, tethered at 1900 psi.... I started at zero gap, and checked the velocity over 4 shots, at each 1/2 turn of adjustment out from there until the valve fell off the cliff....

The results were pretty much as I expected.... The rod restricted the filling of the cavity in the poppet head somewhat, and the gun acted more like it had the 0.028" vent hole without any rod in place.... The velocity was slightly less at zero preload, peaking at 1 turn of gap at 975 fps, and then declining slowly to 2 turns, after which the velocity dropped quite quickly.... It did fall in a more linear fashion over the next turn of adjustment before hitting the basement at 3.5 turns of gap.... I was not at all happy with the ES, however.... It was great while the velocity was on the plateau at 970 fps, but as soon as the velocity started to drop, the ES increased.... At an average velocity of 958 fps, at 2 turns of gap, the ES over just 4 shots was 17 fps (2%).... At 2.5 turns of gap, the average velocity was 872 fps, but over 4 shots varied between 751 - 933 fps (20%)....

I tethered the gun to my 500 cc tank, regulated as before at 1800 psi, and ran one 8-shot string to check the efficiency.... It used 210 psi, producing an average velocity of 953 fps (69 FPE) with a 17 fps ES (1.8%) over the 8 shots.... This is an efficiency of 1.25 FPE/CI, basically unchanged from previous results at that velocity....

The greatest range of adjustability I achieved during these tests was with the 0.028" vent hole and no metering rod in place.... I had a solid 20-25 fps range over which the efficiency was over 1.2 FPE/CI, coupled with a low ES.... It was the closest thing to a conventional "knee" I have been able to achieve with the Cothran valve.... The only way to really adjust the velocity remains changing the pressure.... but that setup allowed me to decrease the velocity below the normally flat plateau the Powerhouse valve displays by up to 25 fps, accompanied by a decrease in the amount of air used.... Trying to tune further below the plateau, with any of these "improvements", resulted in unstable operation and a high to unusable ES....

I am going to try the 0.035" vent version (without rod) at 2900 psi with a heavier hammer.... and also plan to do some testing with it with the .30 cal top end.... once I top up my Great White....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on February 10, 2017, 08:53:17 PM
This evening I got a chance to do a little bit more testing.... I used the .25 cal version with the Cothran valve, with the 0.035" vent hole, but this time I put a 0.8" long piece of 3/32" brass rod inside the valve stem instead of the metering rod.... This is a loose fit, so it won't restrict the HPA entering the head of the poppet, but it will take up a lot of the volume inside the stem.... It is longer than the metering rod by 0.10", and the lenght just clears when the poppet is full open.... I also put the 51 gr. MDS hammer (with steel core) back in, so I did 2 things at once, not the best situation, but I'm running out of the 34 gr. pellets.... I tethered the gun at 1900 psi, determined where zero gap was on the SSG, and shot a couple of shots at each gap setting, increasing the gap until the velocity went over the cliff.... The velocity was pretty much stable, although the ES was poor, until I got to 4.5 turns of gap, when it started to decline, slowly at first, and then rapidly, falling over the cliff at over 6 turns of gap.... The velocity curve was quite similar to what I got with the metering rod in place with the spring, except it moved out 3 turns on gap, which would be due to the heavier hammer.... I tried one string tethered to my 500 cc bottle at 4.5 turns out, and 8 shots averaging 938 fps (67 FPE) used 220 psi of air, which is 1.16 FPE/CI, not quite as good as before....

I then tethered the gun at 2900 psi, and repeated the testing of velocity vs SSG gap.... At this higher pressure, I just nicely had enough hammer strike with the 51 gr. hammer.... I was able to max. out the velocity at 1/2 turn of gap on the SSG, just about perfect.... and the velocity was only 10 fps less than what I got in the very first tests with the valve in stock form.... With the 0.035" vent, however, there was some adjustment to the velocity before the velocity plummeted.... I didn't do enough shooting to determine what the ES was like, just a shot or two at each setting.... but it looks like the larger vent does pretty much the same thing to the curve at 2900 psi as it does at 1900 psi.... It would require a lot more testing to determine the optimum vent hole size at this higher pressure.... and the fact that I was down slightly on velocity tells me that the 0.035" hole is a bit too large.... I'm guessing that if I remove the 3/32" spacer rod, the dwell (and the velocity) will drop a bit more.... I may try that tomorrow....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on February 11, 2017, 01:45:06 PM
OK, today I used the Cothran valve with the 0.035 vent hole and no rod inside the stem.... I still like not having the rod in place, providing you have some method of completely preventing hammer bounce.... The unobstructed flow through the vent hole into the cavity in the poppet seems to provide the smoothest knee, and the tightest ES, IMO.... However, don't expect much usable range of velocity adjustment, you still need to do 95% of that with the pressure.... All the larger vent hole does is provide you the ability to approach the cliff more slowly and under more control.... The combination of a larger vent hole, and no hammer bounce, produces better efficiency.... The larger the vent hole, the shorter the valve dwell, and if you go too big, you will have to increase the pressure to get back the velocity you lose.... With the .035" vent hole, I am losing about 20 fps in the .25 cal. and about 30 fps in the .30 cal. at 1900 psi.... but gaining in efficiency....

I used my 51 gram MDS hammer with the steel core.... This additional hammer mass gave me back most of the velocity I lost when I went from the 0.028" vent hole to the 0.035" one.... This combination is the only one I have found where I can tune for both 1900 psi and 2900 psi, in both .25 and .30 cal, with just the SSG gap, and still have some gap at the higher pressure and yet get to the plateau.... I shot a few shots at each SSG gap setting with the 34.2 gr. pellets in the .25 cal at both 1900 psi and 2900, and did the same with the 50.2 gr. pellets in the .30 cal at both pressures.... Here are the results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%20035%20Vent_zpsndvpcmm5.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%20035%20Vent_zpsndvpcmm5.jpg.html)

The .25 cal is in red, and the .30 cal is in blue.... The solid lines are at 1900 psi, and the dotted lines are at 2900 psi.... As you can see, the .30 cal requires about 1 turn less gap than the .25 cal.... At 2900 psi, you need 3 turns less gap than at 1900.... At the higher pressure I tried a couple of turns of preload (negative gap), and the gun got VERY loud (as expected) and the velocity fell off slightly.... I think that may be due to the O-ring bumper compressing with the heavy hammer strike, and kicking the hammer back slightly faster, reducing the dwell.... I also had something interesting happen with the .30 cal with 2 turns of preload.... The valve went into full auto mode, and completely dumped the 80 cc plenum, firing like a machine gun.... I would suspect that was due to removal of the metering rod, combined with too hard a hammer strike bouncing off the O-ring.... It certainly shows what can happen when you start modding a well-developed product, trying to make it do things it was never designed to do.... YOU REMOVE THE METERING ROD AT YOUR OWN RISK !!! .... Don't even think about doing that unless you have a hammer stop, and a lightweight hammer and springing system that won't bounce.... My guess is that had I still had the Iso-Damp bumper in place, its energy absorbing qualities would not have allowed this to happen....

I also tethered to my 500 cc bottle, with its output regulated to 1800 psi.... I only tested one SSG gap setting in .25 cal, and one in .30 cal, picking a velocity that was just on the low side of the plateau, at the very beginning of the knee.... The reason for that choice, was that as you approach the knee, the ES starts to increase.... This is a consistent effect with the larger vent hole, I think is what is happening is that the valve is becoming unstable when you ask it to operate where it was never designed to.... It can't make up it's mind whether to cycle properly, or to fall over the cliff.... Try as I might, I have not been able to find any combination of vent size and metering rod that produces stable velocities when you tune on the knee.... The only choice I have found, to keep a tight ES, is to tune to the point where the velocity is just starting to fall, at the bottom of the plateau.... This is in reality the same as tuning a stock valve near the top of the cliff.... the difference is that with the larger vent hole, you have less dwell, and greater efficiency, and the SSG gap adjustment is a lot less fussy.... ie it is easier to find the right spot....  Here are the results of the efficiency testing at 1800 psi....

.25 cal. 34.2 gr. JSB @ 4.5 turns of gap.... 946 fps (68 FPE) on 210 psi of air for 8 shots, which is 1.23 FPE/CI.... (should be 46 shots per fill = 3128 FPE total)....
.30 cal. 50.2 gr. JSB @ 3 turns of gap.... 909 fps (92 FPE) on 215 psi of air for 7 shots, which is 1.43 FPE/CI.... (should be 40 shots per fill = 3680 FPE total)....

Note that the shot count is projected from the pressure drop for 1 magazine, and is therefore only approximate.... It is based on a 3000 psi fill, and the 1800 psi setpoint (1200 psi of headroom).... The exact setpoint pressure and velocity and pellet used will affect the shot count, of course.... I tried the 44.8 gr. JSB .30 cal pellets, and they shot about 35 fps faster, with slightly lower efficiency.... I didn't do any testing with BBTs today.... I am pretty sure that I am going to set both BRods up regulated, with Cothran valves, in their final configurations.... Providing they prove to be accurate, it is my intention to increase the pressure slightly for the .30 cal to move the 50 gr. JSBs up closer to 950 fps.... A 2000 psi setpoint should do that nicely, trading off some efficiency and shot count to get closer to the 100 FPE mark....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on February 23, 2017, 06:14:58 PM
Travis sent me a replacement poppet for my Cothran valve, as I think I went too far with the 0.035" vent hole.... because I lost some of the peak velocity.... I tried this one with the stock 0.020" vent hole, but with no metering rod, and it acted normally.... The velocity on the plateau (.30 cal. 50 gr.) was the same as stock, ie removing the metering rod didn't change it.... I had no strange effects like hammer bounce, but remember, I am running a #210 90D O-ring on the back of the valve to limit how far the hammer can drive the stem to about 0.075".... and the O-ring then stops the hammer, absorbing any excess energy.... However, with the small 0.020" vent, the valve was back to being "on or off", with a flat plateau and then a sudden cliff, losing the small amount of adjustment you can get with a bigger vent....

I had previously tried a 0.028" vent hole, which worked fine, and then increased it to 0.035", which IMO is too big, because I lost velocity on the plateau.... I think this means that I cannot get enough dwell to max. out the power.... Both the previous sizes were achieved by a pointed burr in a Dremel, which is difficult to get to the correct size, requiring that you keep checking the hole with a piece of wire of the diameter you want.... A couple of days ago, in a local Home Hardware, I saw some Cobalt twist drill that were 1/32" (0.031"), which is in between what I had tried, so that is what I used to enlarge the hole in the new poppet.... Travis had told me that the shaft of the poppet was very hard, and to grind it with a Dremel.... but I picked up a pair of these drills (they were $6.49 for 2) in the hopes that the cobalt steel would be hard enough to do the job.... I used the smallest collet in my Dremel, and ran it at the lowest speed (still probably 5000 PRM), and it drilled the hole out perfectly.... You have to be careful not to break such a small drill, but it was a lot easier to do than using the pointed burr, and the hole will be the same size, every time....

I was very pleased with the results.... I haven't lost any of the peak velocity on the plateau with the 1/32" vent hole.... This compares with a 35 fps loss with the 0.035" hole.... I haven't yet had the opportunity to see how much of an adjustment range I can get with this size.... ie what the knee looks like.... but I'm sure it will be similar to the 0.028" hole, which gave me some degree of adjustability before the steep dropoff.... Plotting that curve, and checking the efficiency on it, will have to wait for another day....

Bob
Title: Re: Tale of Two BRods
Post by: oneshot61 on February 28, 2017, 06:28:41 PM
That's what I did mine with. But I set up one night and twisted it slowly with my fingers until I broke through. I still broke one of the bits, which is very easy to do. I think my stronger valve spring has taken a bit to much off the top power though. Looking forward to your results.
Title: Re: Tale of Two BRods
Post by: rsterne on March 11, 2017, 07:06:56 PM
The first trials with the new stem with the 0.031" (1/32") vent hole were a bust.... I removed the metering rod, and over a matter of a few shots at 2900 psi the velocity started to drop.... I had to keep increasing the hammer strike, and even that wouldn't put me back to where I started.... I pulled the valve apart, and found that the seat had a deep groove in it.... I can only assume that by removing the metering rod the valve was closing with such force it destroyed the rather soft seat on the poppet.... Either that, or there was a leak in the force reduction piston O-ring, which put a lot more force on the poppet.... I don't know why I never experienced this with the original poppet, it was still in good shape.... The solution was to disassemble both poppets and build one good one from the two sets of parts....

The poppet is made in three pieces, the hollow stem, the seat, which looks like a nylon washer, and the tubular front part, which is the sleeve of the force reduction system....The two metal parts are threaded together using 10-32 threads and glued, which make the poppet difficult to take apart without scarring the surfaces.... By using the two chucks on my lathe, and turning the headstock backwards by hand, I was able to take the poppets apart.... I used the new stem, with the 1/32" vent hole, and the old seal, turned over to use the flip side, which was perfect, and one of the front sections.... I reassembled it with a drop of blue Loctite and let it cure overnight before assembling and pressurizing it.... It sealed up perfectly first try.... I had installed the stock metering rod, and set about testing it....

As I found previously at 1900 psi, the velocity was right back up to where it was with a stock vent hole.... In .25 cal, there was very little adjustability, basically a plateau and a cliff.... In .30 cal, there was a slight rounding of the edge of the cliff, but the valve was still rock stable just above the dropoff.... With 70 gr. bullets, I did lose a few fps, so there is some indication that this is the largest vent hole you can use in .30 cal at this pressure without losing performance.... I would not go larger, because with the 0.035" vent I lost about 20 fps.... I did some short strings (1 magazine) tethered to my 500 cc tank with the output regulated at 1900 psi, and the efficiency was slightly better than with either the stock vent hole, or with the 0.035" vent, so I think I hit the sweet spot for the vent size, at least when regulated at 1900 psi.... Here are the results....

.25 cal. 34.2 gr. JSB.... 987 fps (74.0 FPE) @ 1.00 FPE/CI, with an ES of 13 fps....
.25 cal 46.4 gr. Cast RN.... 878 fps (79.5 FPE) @ 1.04 FPE/CI, with an ES of 7 fps....
.30 cal 44.8 gr. JSB.... 971 fps (93.7 FPE) @ 1.11 FPE/CI, with an ES of 12 fps....
.30 cal 49.3 gr. Daystate.... 949 fps (98.6 FPE) @ 1.17 FPE/CI, with an ES of 12 fps....
.30 cal 70.0 gr. BBT.... 824 fps (105.7 FPE) @ 1.35 FPE/CI, with an ES of 11 fps....

The .25 gr. pellets required 6 turns of gap on the SSG, the .30 gr. bullets required 5 turns, and the other three all were shot at 5.5 turns of gap.... I can probably get a bit smaller ES by using a lighter hammer, a weaker hammer spring, or a bit less preload on the SSG, to reduce the gap.... I was running the 51 g. MDS hammer with the steel core....

I then took the gun all apart, stripped down the valve, and replaced the metering rod with one I had sanded down 0.003" smaller.... I had heard this was something worth trying, and it produced some interesting results.... First of all, it created a curve where the plateau used to be.... With no gap in the SSG, the velocity dropped about 15 fps with the .25 cal 34 gr. JSBs, and about 40 fps with the .30 cal 50 gr. JSBs.... It then increased until there was 3 turns of gap, and then curved downwards to about 6-6.5 turns and was in the basement when 7 turns out.... I think the lower velocity at heavy hammer strike may be because of the hammer bouncing off the rubber O-ring, although why it should show up only with the undersized metering rod, I have no idea.... The total adjustment range between peak velocity (at 3 turns) and when it rolled over to head into the basement was about 100 fps, so I was quite excited that I would finally be able to get some adjustment in velocity with the Cothran valve without having to play with the pressure.... Unfortunately, for nearly all of that 100 fps range, the velocity was unstable, with the ES increasing as you approached the cliff.... In other words, with the undersized metering rod, I got a slight knee, but not a usable one, as the ES quickly became unusable.... Just before the velocity took a dive, the ES could be as much as 130 fps from one shot to the next.... I fiddled with it, trying various adjustments, but could never get the ES as low as with the stock metering rod, so I took the gun apart and put the stock rod back inside the valve stem....

I tried a few more tests with the stock metering rod and the 1/32" vent hole, and I am very pleased with this combination at 1900 psi.... As long as you stay just above the cliff, in the area where the velocity is 10-20 fps below the maximum at that pressure, you are rewarded with a narrow ES, lots of power without maximum report, and decent efficiency.... I don't think there is anything I can do to get a better tuning range than I have for the Cothran valve, in .25 or .30 cal, when regulated at 1900 psi....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on March 12, 2017, 11:52:07 AM
I took a few shots today tethered at 2900 psi, with the following results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Cothran%202900%20psi_zpsm0blqx5z.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Cothran%202900%20psi_zpsm0blqx5z.jpg.html)

As you can see, the pellets that were in the mid 900s at 1900 psi are Supersonic at 2900.... I tried some heavier bullets, sized down to fit, and the biggest surprise was the 66 gr. in 25 cal breaking 120 FPE.... I have a feeling that the enlarged vent hole in the stem is hurting the performance of the 109 gr. in .300 cal, as I would have expected more FPE from it instead of less.... After all, the porting is the same as my DAQ, which shot over 180 FPE with the same bullet at the same pressures.... If you correct for my shorter barrel lengths, my .25 cal is about on a par with Lloyd's original experiments with the MRod with the Cothran valve, as is the 80 gr. bullet in the .30 cal, but the 109 gr. is lagging.... It could also be the O-ring bumper on the back of the valve that I have used to limit the hammer travel, I have, after all, done several things to throttle back the valve to work better regulated at 1900 psi.... I guess it's not to surprising that some or all of those changes have combined to knock the top end off the power at the top end.... in fact it would have been surprising NOT to see that....  ::)

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on July 31, 2017, 08:26:30 PM
I know it has been a while since I posted in this thread, but summer is an impossible time for me to work on airguns because the Motel is too busy.... During the winter, I worked with Travis and Jim designing an adjustable regulator to go inside their drop down tank block, as used in the new COBRA.... I just received one in the mail today, and it is gorgeous.... It threads right into the WAR tube for the FLEX/WARP/COBRA....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Regulated%20Tank%20Block%20Right_zpssy2kxlsk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Regulated%20Tank%20Block%20Right_zpssy2kxlsk.jpg.html)

I got both tank adapters, one for 5/8"-18 UN threads, and one for 18 mm x 1.5 mm threads, so I can use any tank.... The burst disc is on the output side, and is a 3K, as I won't be using more than about 2200 psi.... However, I understand the output can be adjusted higher than that, depending on the Bellevilles installed....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Regulated%20Tank%20Block%20Left_zpsoho5cabk.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Regulated%20Tank%20Block%20Left_zpsoho5cabk.jpg.html)

It has room for two gauges, the upper one reads output pressure, and the lower one tank pressure.... The adjusting screw is an allen set-screw on the bottom of the block.... It moves the HP seat towards the piston (CW) to reduce the output pressure and away from the piston (CCW) to increase it.... I can't wait to try it out on the tube I have the Cothran valve installed in.... It will be the perfect arrangement for that, because you must adjust the pressure to adjust the velocity....

Bob
Title: Re: Tale of Two BRods
Post by: Alan on August 01, 2017, 04:20:17 AM
I have one of these adjustable regulators on the Cobra version I bought from Travis earlier this year. The results of the team effort are rather evident, and thanks to all who made the device possible.

Once you play with it a bit, it is really easy to readjust the pressure—handy if you shoot different weight pellets. The only issue, and Travis warned me about this, is when you do adjust the regulator, GO SLOW! Itsy-bitsy movements is all it takes! Even a 5° rotation can make the adjustment too much!

I want to add something here. Bob, you truly are an unsung hero. I've never met you in person (I'd like to sometime), but your dedication and thoroughness in answering questions is legendary here, and on just about every other shooting-related web site out there. If I could bestow a gift on you, it would be a Doctorate of Letters in airgun technology! You sure have earned it!
Title: Re: Tale of Two BRods
Post by: rsterne on August 01, 2017, 08:28:49 AM
Thanks for the kind words, Alan.... When I started in airguns a decade ago, there was very little GOOD information on the Forums, people were not documenting and sharing their ideas, for the most part.... I struggled trying to get helpful information (with a few important exceptions, by people I will forever be in debt to).... so I decided early on to do the best research I could, and share all my results, good and bad, as accurately and completely as I could.... I am delighted that effort has been valued, and I hope it will continue to survive, despite Photobucket's recent efforts to derail the knowledge sharing on our Forums....

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on August 01, 2017, 11:56:19 AM
 Photobucket arrrrgggghhhhhhh!!!!!!!! :( >:(
Title: Re: Tale of Two BRods
Post by: rsterne on January 16, 2018, 09:14:11 PM
This project has been on the shelf over the summer, both for lack of shop time and because I have been waiting to received one of the new ART/SS valves to try.... The hope is that it will match the Cothran, both in performance and ease of opening.... with the added benefit of being able to adjust the velocity with hammer strike, something you can't do with the Powerhouse valve.... you have to change the pressure to change the velocity.... Anyways, the wait is over and my valve arrived today, many thanks, Travis....  8)

The valve is a stock JSA "SS Balanced Valve" as they supply for the MRods.... It comes with a 3/16" exhaust port and the stock recess for the transfer port, which would not work in my BRods, as they are set up for a 3/8" OD transfer port with a 1/4" exhaust port.... Travis assured me that there was plenty of meat to enlarge the ports, and there certainly was.... I usually angle my exhaust ports about 20 deg. but with that big a port and no experience with this valve, I choose 15 deg. instead, and I'm glad I did.... At 20 deg. with a 1/4" port, I think I would have broken into the back of the valve and ruined the seat.... The valve throat is 0.281", which works out to the same area, once you subtract the 1/8" stem, as the 1/4" exhaust ports.... This is the same size throat as what I had on my modded MRod valve with the PEEK poppet, but the area is smaller than the Cothran valve.... I didn't want to drill out the throat at this time, but I did blend the new 1/4" exhaust port into the throat with a spherical Dremel burr.... There is certainly lots of port area for lots of flow....

I got the valve installed in the tube for one of my BRods and it seems to be holding pressure.... I will leave it overnight and plan on doing extensive testing tomorrow, tethering the gun at 1900 and 2900 psi in both .25 and .30 cal to get the baseline preload curves and assess what the opening forces are like compared to the Cothran valve and my modded MRod valve.... This should be FUN !!!

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 17, 2018, 03:45:17 PM
Here is the first set of results for my BRod .30 cal with the ART/SS valve installed.... I tethered it at 3000 psi (a more accurate, digital gauge says my regulator was not set for 2900 as I previously thought), and tried the 50 gr. JSB/Daystates and also the 67 gr. NOE BBTs.... I tried all the SSG settings from maximum preload (way too much), through zero gap, to 10 turns of gap (over 1/2").... I then repeated the procedure with the 45 gr. JSBs and 50 gr. JSB/Daystates tethered at 1900 psi.... Lastly, I connected up my 500 cc bottle which has a regulated 1900 psi output and shot one 7-shot magazine of the 50 gr. pellets at several gap settings to find the pressure drop and calculate the efficiency.... Here are the results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20ART-SS%20Gap_zps5icyu4tb.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20ART-SS%20Gap_zps5icyu4tb.jpg.html)

First some comments about this valve.... IT OPENS EASILY.... nowhere near the hammer strike required of my modded MRod valve.... I will be doing the same testing procedure with my Cothran valve to get an idea of the relative hammer strike required, but don't have that data yet.... It is much more responsive to changes in hammer strike than the Cothran, although still exhibits a VERY sharp velocity drop if you try and tune it for tiny sips of air (ie low velocity).... This sudden drop could well be due to the jet size installed in the inlet of the valve, I only got one with the valve, presumably a "stock" one, whatever that is.... and I can tell you it's pretty tiny.... With that tiny jet, and the huge drilled out exhaust port, I may be operating the valve outside its normal parameters.... in fact you can almost bet on it.... I hope Travis has some ideas to try and will send me some other jets to play with.... not that it really matters, I never tune my guns on the downslope anyways.... If I wanted a lower velocity, I would reduce the regulator setpoint and move back up onto the knee of the curve....

I am using an MDS hammer with a 3/4" steel core that weighs 51 grams.... The hammer spring is 0.48" OD x 3.00" long, and is made of only 0.051" wire, so has a spring rate of just 8 lb/in.... It is currently set up on the SSG with 0.60" of preload (4.8 lbs.).... and when set to zero gap, with the hammer stroke I have of 0.79" takes a maximum force of only 11 lbs. to cock the gun.... If you notice from the data in the graph, I can run the SSG gap at about 6 turns out (0.33") at 1900 psi (cocking force 8.5 lbs) and about 3 turns out (0.165") at 3000 psi (cocking force under 10 lbs) with hardly any velocity loss.... Those settings are basically at the top of the "knee".... With the 50 gr. pellet at 1900 psi, at 6 turns out, the velocity is 922 fps (94 FPE) and the efficiency is 1.04 FPE/CI.... The knee is quite long and gentle, making velocity adjustment quite insensitive, until you approach the "cliff".... Just before you get there, the velocity seems to get unstable, and the ES increases.... and then suddenly you are teetering on the edge of the cliff, where just a quarter turn more gap and the velocity tanks to under 400 fps....

The maximum performance (plateau velocity) with this valve is a few fps better than my modded MRod valve or the Cothran valve at 1900 psi.... and virtually the same with the 67 gr. BBT at 3000 psi.... but with the 50 gr. pellet at 3000 psi it was about 30 fps faster (1100 fps).... However, it also had virtually no velocity drop as you increased the SSG gap until it suddenly fell off the cliff.... almost acting like a Cothran valve.... However, this is so far out a normal condition (50 gr. pellet at 1100 fps) it doesn't really matter.... it's more an anecdote.... One other thing of note.... If I reduced the SSG gap to negative (ie introduced preload) the air consumption, report, and recoil all went "stupid".... I can only assume that the closing forces on the balanced poppet are so small that they are overwhelmed by the 5 lbs. preload on the SSG, and it increases dwell to the point the valve is still wide open when the pellet leaves the muzzle.... and YES, it's THAT dramatic.... When I was testing the pressure drop with 2 turns of preload, I actually got 640 psi of drop in my 500 cc bottle in just 3 shots.... compared to 370 psi drop in 7 shots with zero SSG gap.... Pretty much BOOM when you pull the trigger, complete with 6" or more of muzzle jump....  :o :o

The 8 lb/in. spring is OK for use at 3000 psi, but realistically I need to either reduce the preload on the SSG, or fit an even weaker spring for use at 1900 psi.... The SSG gap is too large at that pressure, and I might find a velocity difference shooting up or downhill from gravity slowing the hammer.... This change would make the gun even easier to cock, which seems silly, as it's sooooooooo easy now.... I can tell you, I'm SURE impressed at the reduction in cocking force with the ART/SS valve.... Travis and Lloyd sure came up with a winner here.... I can see that I will end up converting all my Big Bores and bullet shooters over, to get rid of the massive, long stroke, hard to cock hammers.... Incidently, I resized a 109 gr. Lee HP in .308 cal down to 0.300", and although it was still hard to chamber, I got 811 fps with 2 turns of preload (159 FPE) at 3000 psi.... accompanied by a huge roar and muzzle jump.... Yes, this valve can move a LOT of air....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 18, 2018, 11:46:38 AM
Here is the data for the .25 cal BRod using the ART/SS valve.... The methodology was the same as for the .30 cal.... except the pellets used were the 25.4 gr. Kings and 34.1 gr. King Heavies at 1900 psi and a 52.7 gr. RN .25 ACP bullet at 3000 psi.... Here are the results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2025%20ART-SS%20Gap_zpsriqobzml.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2025%20ART-SS%20Gap_zpsriqobzml.jpg.html)

The SSG gap where the gun fell off the cliff was virtually the same at the same pressure, about 7 turns at 3000 psi and 9 turns at 1900 psi.... I was using the same hammer and spring, all that changed was the upper (receiver and barrel).... This gun drives the Kings way too fast, nearly Supersonic at 1900 psi, but the King Heavies look to be a great choice at this pressure.... At 7 turns of gap (just over 3/8") the velocity is 966 fps (70.7 FPE) but the efficiency is a bit low, at only 1.01 FPE/CI.... Still, this is pretty impressive performance at only 1900 psi, and should yield about 32 shots at 70 FPE from the 500 cc bottle.... nothing to sneeze at....

As a bullet shooter at 3000 psi, the gun is solidly over 100 FPE, peaking at 115 FPE.... This is the highest FPE (by a whisker) I have seen with the .25 cal BRod at this bullet weight, and with a 60 gr. bullet would be even higher I am sure.... I didn't do any efficiency testing at that pressure, as I am short of cast bullets at the moment, and don't want to stop testing to make more.... Once again, if you crank in actual preload on the SSG, the gun roars and kicks as it blows air out the muzzle after the bullet is long gone.... It appears obvious that this valve (at least with the big ports) needs either an SSG or SSS to have any chance of behaving in a civilized manner.... It does offer some range of velocity adjustment, and the efficiency, like the Cothran valve, is best when operating just above the cliff.... However, with the ART/SS valve, that range is a lot broader and easier to tune to....

With the ART/SS valve using a 1/4" exhaust port, my BRods will be great with pellets when regulated at 1900 psi.... and are capable of shooting with bullets in both calibers at 3000 psi.... I'm pretty please with the results for initial testing.... I do need to try less preload on the spring to try and reduce the gap on the SSG, particularly when regulated.... I hope to get to that soon....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 18, 2018, 04:25:37 PM
I reassembled a BRod with the Cothran valve this afternoon just to assess the comparison between the required hammer strike with it and the ART/SS valve.... To my surprise, the new ART/SS valve was easier to open than the Cothran....  :o .... Even with the preload reduced to only 0.40" (3 lbs.), the Cothran valve fell over the cliff at a 3 turn smaller gap than the ART/SS valve, with the same pellet at the same pressure.... Now BOTH these valves are a LOT easier to open than a conventional PCP valve of the same dimensions.... That is the big advantage to balanced valves, you can use huge ports, throat and poppet, and not have to end up with a gun that is impossible to cock....

I rechecked the Cothran valve, and it remains stubbornly "ON" or "OFF".... You really have no control over the velocity with the hammer strike, you need to change the setpoint pressure to do that.... Yes, the Cothran valve uses less air when tuned just above the cliff, but it cant be turned down a bit before it ceases to cycle properly and the velocity drops to near nothing.... It is when operating just above the cliff that the ART/SS valve can be tuned for good efficiency while remaining stable (unless you get too close to the cliff, as mentioned earlier).... That region with the Cothran valve is very narrow, and when you get close to the cliff the velocity becomes unstable, although if you get it just right, it also exhibits improved efficiency.... It is just way fussier to adjust than the ART/SS valve....

To make large adjustments to the velocity with the ART/SS valve (at least in my large ported version) you still need to alter the setpoint pressure.... However, having a 100-200 fps range of adjustment without changing the pressure sure makes it easier to find a suitable tune.... It seems that the heavier the bullet, the wider the velocity adjustment range.... I suspect that with a stock ported ART/SS valve the adjustment range might be even wider.... It looks like I may have to find a weaker spring to reduce the SSG gap down to the desired level when running regulated at 1900 psi.... but before I make that change, I think I will completely remove the front jet and see what happens....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 19, 2018, 12:47:19 PM
Today I tested the ART/SS valve without any jet on the inlet side.... just about a 1/8" hole there.... I still had the preload on the 8 lbs. hammer spring on the SSG set to 0.40" (about 3.2 lbs).... I tested the .30 cal version with the 50 gr. pellets at 1900 psi (only), and realistically there was no significant difference with the jet removed.... The valve still took very little hammer strike to open it.... So, I then swapped out the MDS hammer with the steel core (51 grams) for one with an aluminum core that only weighed 27 grams.... For some unexplained reason I lost about 10 fps from the maximum velocity (which I would not tune for, it would be too inefficient).... but as expected I now needed less SSG gap to get to the cliff.... Here are the results, compared to where I started with this valve (black line)....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20ART-SS%20%20No%20Jet%20Gap_zpsbm6ecxjy.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20ART-SS%20%20No%20Jet%20Gap_zpsbm6ecxjy.jpg.html)

Changing to the 0.40" preload from 0.60" is what moved the top of the cliff from 9 turns of gap to 8 turns.... I didn't plot that curve because it essentially tracked the black line except for the earlier cliff.... You can see that with no jet installed (purple line) there was less of a "knee" to the curve.... still some, but there was less velocity adjustment before you got to the cliff.... The same setup but with the 27 gram hammer (the orange line) shifts the cliff to only 5 turns of gap, but I can still reach the plateau with 1 turn of gap.... This gives me an adjustment range of 4 turns, and makes the amount of gap where I would adjust the gun just about where I like to see it.... around 1/8"-3/16".... The only way to reduce it further would be a lighter hammer spring, or reducing the hammer stroke.... I can actually DO that with the aluminum cored hammer, as it has a steel setscrew insert for the striker (currently set flush).... One other thing I noted with the very light hammer.... The range of velocity adjustment between plateau and cliff increases significantly.... leading me to believe that light hammers and this valve would be a great combination....

I did one "efficiency run" by shooting one 7-shot magazine with the velocity set to just over 900 fps with both setups.... Small changes in the exact velocity make big changes in the efficiency at around that velocity with these big ports.... but essentially I believe there is little difference in the efficiency if the velocity is the same with the jet removed.... HOWEVER, it does give you less velocity adjustment just above the cliff, and if you are tuning for efficiency I think you would struggle to get the best combination of power and air usage without the jet.... If all you are interested in is pure power with a light hammer strike, however.... this valve is a BEAST.... It requires MUCH less hammer strike than even the Cothran Powerhouse valve in the testing I have done so far.... I'm impressed....  8) 8) 8)

Bob
Title: Re: Tale of Two BRods
Post by: oldpro on January 19, 2018, 08:27:16 PM
 Your Data is a welcomed sight from many hours of hard work. Thanks Bob.
Title: Re: Tale of Two BRods
Post by: rsterne on January 21, 2018, 07:35:52 PM
Today I assembled the regulated tank block I got from Travis back in the summer.... It went well, and after a short learning curve installing shims, I was able to adjust it from 1000 psi up to over 2000.... I didn't try and go higher, but I am sure it will.... It has a 3K burst disc on the output side, and I didn't want to push it.... The adjustment is quite sensitive, you don't have to turn the 10-32 adjusting setscrew very far to move the output by 100 psi.... maybe 1 flat on the allen key or less....

Since the Cothran valve cannot be adjusted using hammer preload (or SSG gap), and needs to have the pressure adjusted to change the velocity, or retune for a different pellet weight.... it was a perfect match for an externally adjustable regulator.... Since there are two excellent pellets made by JSB that are quite different in weight (25.4 gr. and 34.1 gr.) I decided that to install the .25 cal upper on the lower that used the Cothran valve and the adjustable regulated tank block and I installed a 500 cc, 3000 psi bottle on it.... My initial adjustment of 2000 psi drove the 34.1 gr. JSB King Heavies at over 980 fps, but I used the opportunity to find out where the cliff was, and where the SSG gap needed to be adjusted to be close to the cliff, but solidly on the plateau, where the valve is operating stably.... That was with 2 turns of gap.... Then I shot the tank down to about 1700 psi so that I could drop the setpoint adjustment....

When increasing the setpoint pressure, you back out the 10-32 screw, which lowers the HP seat, moving it away from the piston and Belleville stack.... The seat opens, allowing more air to flow to the output side, raising the pressure and pushing the piston towards the (now lower) seat, against the Bellevilles, compressing them until the seat closes at the now higher pressure.... This puts no additional load on the seat, and can be done at any time.... When you want to decrease the output pressure, however, you need to drop the tank pressure below not only your current setpoint, but also below where you want the new setpoint to be.... The reduced pressure on the piston allows it to move away from the seat, and this allows you to turn the 10-32 screw in without putting additional pressure on the seat and possibly damaging it.... I wanted to start at 1800 psi and work my way back up, so I drained the tank down to 1700 and turned the 10-32 adjuster in until I felt slight additional resistance when the seat contacted the piston.... If you do this carefully and slowly, you can feel when they make contact.... When I added more air to the bottle, the gauge on the output side of the tank block moved up slightly, to about 1800 psi.... I shot a few shots, and the velocity was down to about 920 fps, so I simply backed the 10-32 adjusting screw out a fraction at a time, shooting a couple of shots at each setting, until I got my target velocity of 950 fps.... I then shot a couple of shots at each SSG gap setting, and recorded the results, which are on the graph below in red....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2025%20Cothran%20Regulated_zpsled0azhx.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2025%20Cothran%20Regulated_zpsled0azhx.jpg.html)

You can see the typical "cliff" exhibited by the Cothran valve which starts just before 3 turns out.... The velocity at 3 turns out is very unstable, with an ES of nearly 200 fps, because the valve is about to fall over the cliff.... However, at 2 turns of gap, it is rock solid, with about a 1% ES.... From previous experience I know that is the optimum place to run a Cothran valve, with the lowest hammer strike that allows stable operation and low ES.... I tried the 25.4 gr. pellets, and the velocity was over 1050 fps, so to get them to work I knew I had to lower the setpoint pressure.... I started simply shooting the 25.4 gr. pellets and watched the velocity fall as the pressure dropped.... I was pretty shocked to discover that to get down to 950 fps I had to drop the pressure in the tank all the way down to 1400 psi.... I shot a few more shots, to drop the tank pressure to 1300, and then turned in the 10-32 adjusting screw until I could feel it contact the seat.... I added air to the tank, the output gauge barely budged, and the velocity settled in at about 910 fps at about 1300 psi.... I slowly backed out the pressure adjusting screw, shooting a couple of shot at each adjustment, and stopped when the velocity with the 25.4 gr pellet reached my target of 950 fps.... The gauge indicated 1400 psi.... and I confirmed that by shooting the tank down until the velocity just started to drop, while the tank was still connected to the accurate gauge on my Great White.... Yes, I was getting 51 FPE at only 1400 psi.... I ran through the gap adjustments, and recorded the other curve (in blue) on the graph above.... The optimum gap was at 3 turns out, and the cliff started at 4 turns out, 1 turn more than at 1900 psi.... As expected, the valve requires a bit less hammer strike at 1400 psi than at 1900.... I also shot a few of the 34.1 gr Heavy pellets at that same setting, and that velocity is shown on the graph above as the black dot (872 fps).... So, with the 34.1 gr. pellets, I was getting 57.6 FPE at only 1400 psi.... pretty remarkable, and no adjustment made from the 950 fps setting with the 25.4 gr Kings....

Now that I knew that 3 turns out was the optimum setting for the 25.4 gr. Kings at 1400 psi, I recorded the pressure in the 500 cc bottle (using the gauge on my Great White), and shot 8 shots, on regulator, at 1400 psi.... I averaged the velocity (952 fps = 51.1 FPE), and recorded the pressure drop, which was 200 psi.... That works out to 0.97 FPE/CI, which is pretty low, but we are in new territory here, getting 51 FPE at only 1400 psi.... I repeated the test using the 34.1 gr. Heavies, and as I expected, the pressure drop was exactly the same, at 200 psi.... Since the energy per shot increased to 57.6 FPE, however, the efficiency increased to 1.10 FPE/CI.... I then backed out the 10-32 pressure adjuster to increase the setpoint back to 1900, set the SSG gap at 2 turns, and shot another 8-shot magazine at that setting with the 34.1 gr. Heavies.... The pressure drop was just over 200 psi, so I recorded it as 210 psi, and with the average velocity of 950 fps (68.4 FPE), that works out to an efficiency of 1.24 FPE/CI.... pretty decent at that power level....

The pressure drop per shot for all these tunes runs just about 25-26 psi per shot from the 500 cc bottle.... If we use a fill pressure of 3000 psi, with the 1900 psi setpoint, that should give 42 shots at over 68 FPE with the 34.1 gr Heavies.... and with the 1400 psi setpoint, that should give 64 shots at 51 FPE with the 25.4 gr. Kings and nearly 58 FPE with the Heavies.... I think those are quite acceptable numbers, and tuning back and forth between the 25.4 gr. and 34.1 gr. pellets (both at 950 fps) requires only resetting the external regulator adjustment, and one turn on the SSG gap.... In fact, if you don't care about getting the full 64 shots at the 1400 psi setting, you don't even have to change the SSG gap, you can leave it at 2 turns, and just lose a few shots.... If you have the gun tuned at 1400 psi, you can shoot the Kings at 950 fps and the Heavies at 870 fps, for the same number of shots, with NO adjustment necessary....

Bob

Title: Re: Tale of Two BRods
Post by: rsterne on January 22, 2018, 01:33:42 PM
Today I worked on a new SSG to go inside the AR style stock adapter I made a while back.... I had to shorten up the adjusting bolt and spring guide so that it wouldn't interfere with the stub on the stock, as this is a paintball stock and uses a plastic slider.... This version uses a PRod trigger with a taller sear from Lloyd at AirGunLab to work with the thicker MRod tube.... The forestock is a simple piece of ABS plastic pipe slide over the main tube and secured with setscrews.... Here is what the finished gun looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/25%20cal%20BRod%20AR%20Cothran%20Valve%20and%20Adjustable%20Regulator_zpsr0uhj1mh.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/25%20cal%20BRod%20AR%20Cothran%20Valve%20and%20Adjustable%20Regulator_zpsr0uhj1mh.jpg.html)

The 500 cc tank is heavy, so the all up weight is 9.5 lbs including the scope and rings, so the bare gun is about 8 lbs.... If you hold it with your hand just behind the tank block, it balances right there.... It uses the Cothan valve and the Cobra tank block with externally adjustable regulator.... It is currently tuned to shoot the 34.1 gr. JSB King Heavy MkIIs at about 950 fps (68 FPE), for about 40 shots per fill.... With the Cothran valve, the easiest way to adjust the velocity is with the regulator.... the pressure adjustment (currently 1900 psi) is a 10-32 setscrew on the bottom of the tank block.... The barrel is a LW Polygonal, 23.8" long, and fitted with a Hatsan Air Stripper.... The MROd receiver was bored out about 1.5" to accept the larger diameter barrel.... so the free floated barrel is very rigidly mounted to the receiver.... The bolt was fitted with a 3/32" diameter probe, making the chamber area the same as the barrel and transfer porting, which is 0.234"....

All in all, I am very pleased with the way this turned out.... It is easy to cock, with the SSG having 3 lbs. of preload on an 8 lb/in spring.... The 51 gram MDS (steel cored) hammer has 0.79" of stroke, and the SSG gap at this tune is 2 turns, so the cocking distance against the spring is 0.67", making the maximum cocking force less than 8.5 lbs.... About the only thing that would be a nice addition is a BiPod mount on the bottom of the tank block.... My thanks to Travis and Lloyd for their help in procuring the parts for this build, without them it would not have been possible....

Bob

Title: Re: Tale of Two BRods
Post by: oldpro on January 23, 2018, 02:21:13 PM
 Thats a nice looking rig with all the newest tech. installed.
Title: Re: Tale of Two BRods
Post by: rsterne on January 23, 2018, 07:15:55 PM
Today I took apart the other lower, with the ART/SS valve in it, and cleaned it up and reinstalled the #87.5 jet that it came with.... After a couple of experimental settings of the hammer stroke and SSG preload and gap, I ended up using the 27 gram hammer with the striker set flush with the front face.... I lowered the preload to 0.37" (just 3 lbs.) and I was running low on my supply of 50 gr. JSBs, but I had a tin of the 45 gr. FX (JSB) pellets, so I used those to collect the data of velocity vs. preload, with the following results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20ART-SS%20New_zpsol3rxmcb.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20ART-SS%20New_zpsol3rxmcb.jpg.html)

The combination of the stock jet and the very light hammer gave me a much nicer curve, with a full 200 fps of velocity adjustment before the valve fell off the cliff.... This is the widest range I have seen with the SS valve.... Once again, as soon as there was negative gap (preload) on the SSG, the gun became an instant air hog, and barked and kicked like a big angry dog.... However, as soon as there was any gap at all, the report was sharp and crisp, and just gradually became quieter as the velocity dropped, exactly like a conventional valve would do.... I set the SSG gap at 2 turns (just under 1/8") and tethered the gun to my 500 cc bottle with the output regulated at 1900 psi (actually just under).... I left the bottle tethered to the gauge of my Great White (tank valve closed), so that I could check the pressure drop to measure the efficiency.... I did two 7-shot mags. and got an average of 940 fps (88.3 FPE) with about a 1% ES, and the pressure dropped 250 psi for each mag., which works out to an efficiency of 1.18 FPE/CI.... Without changing any settings on the gun, I tried a 7-shot mag. with the 50.2 gr. JSBs I had remaining, and recorded an average velocity of 886 fps (87.5 FPE), but the pressure dropped only 200 psi.... Very surprised by that, I repeated the test, with exactly the same results.... That works out to 1.46 FPE/CI, which is pretty incredible for a .30 cal at that power level....

There is something different going on with this valve, that may be the key to some of the high efficiency numbers we are seeing.... I don't know if it has to do with the reduced velocity, or the slower pressure decay that causes in the valve throat.... but I have never seen such a drastic increase in efficiency before with only a 10% increase in pellet weight.... Normally you would expect the valve to release slightly less air with the heavier pellet, because it "uncovers" a shorter barrel length during the valve dwell, which essentially stays the same, and that results in a slight increase in efficiency.... For some reason, with the heavier pellet, this valve used less air.... a LOT less air, a drop of only 200 psi with the 50 gr. pellet compared to 250 psi with the 45 gr.... I am at a loss to explain why.... Perhaps the higher the pressure in the exhaust port the faster the valve closes, increasing the efficiency.... I don't know, but I like it....  8)

I would like to increase the velocity with these two pellets a bit, so I think I will add a thin shim to the regulator to bump the setpoint a bit.... I would like to be able to adjust the velocity of the 50 gr. between 900-940 fps and the 45 gr. between 940-970 fps just by changing the SSG gap, and not have too big a gap (or too small).... I wish I had another Cobra tank block, with the externally adjustable regulator, but it is more important for that to be paired with the Cothran valve, which has no velocity adjustment expect by pressure.... At least I will have no worries about getting enough hammer strike with this valve.... the gun is very easy to cock, and I have lots of preload adjustment available, with only being at 3 lbs. at the moment....

My biggest problem now, is that I have been burning through pellets like crazy.... and so much air I had to rebuild my ShoeBox a couple of days ago (I got 90 hours on the HP O-rings in my Freedom 8, not bad).... Still, doing lots of shooting and collecting lots of valuable data is worth spending a few bucks, right?.... I hope my wife agrees....  ::)

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 24, 2018, 02:28:20 PM
I had a bit of an epiphany last night about how to tune this valve.... When I looked back over how far below the plateau velocity I generally tune my regulated guns, it turns out that about 3-4% is typical.... By the time you are 5% or more below the plateau, the velocity starts to show a significant increase when the pressure drops below the setpoint.... If you tune less than 3% below the plateau, the gun tends to use more air for not much increase in velocity.... and of course at the plateau it becomes an air hog.... So, this morning I hooked by regulated 500 cc bottle to the .30 cal BRod with the ART/SS valve in it, and did some experimenting.... but I made one (hopefully last) change first.... I made a slightly heavier hammer, that weighs 39 grams instead of the 27 gram I was running yesterday.... This is in between that and the 51 gram hammer I installed in the BRod with the Cothran valve.... The reason for the slightly heavier hammer is that I could not quite get to the plateau velocity with the 27 gram hammer without decreasing the SSG gap below zero (ie adding preload).... which wasted HUGE amounts of air.... I wanted to be able to get to the plateau at zero gap, and adding a bit of weight to the hammer seemed the best way.... and it worked great....

I had checked the output of my 500 cc regulated bottle, and it was actually 1850 psi instead of 1900.... Using that, I plotted a new velocity vs. preload curve with both the 45 gr. and 50 gr. pellets, and got a plateau of 972 fps with the 45 gr. and 945 fps with the 50 gr.... The valve fell off the cliff at 9 turns of gap, with an adjustable range of about 150 fps before it did that.... I tried a few gap settings around 3-6 turns out, and found that at 5 turns of gap, if I let the tank pressure fall below the 1850 psi setpoint I was getting a slight bump in velocity, just as I expected, peaking at about 1780 psi before declining.... That is EXACTLY what I was looking for, my normal tuning point where the shot count is extended a bit below the setpoint pressure, but with a velocity increase of less than 1%.... The problem was, it was occurring at about 940 fps with the 45 gr. and about 880 fps with the 50 gr. pellets, and I wanted a bit more than that.... The solution was to drain the bottle and increase the setpoint pressure a bit.... On the third try I got the shim stack just right, and the new setpoint is exactly 1950 psi.... I repeated the testing with this higher setpoint, with the following results....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%2030%20ART-SS%201950_zpsbnmtb6e0.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%2030%20ART-SS%201950_zpsbnmtb6e0.jpg.html)

As you can see, the plateau velocity is higher, as you would expect with the 100 psi higher setpoint.... Is it now 988 fps with the 45.0 gr. pellets (97.6 FPE) and 954 fps with the 50.2 gr. (101.5 FPE).... and I can get there with a turn of gap in the SSG.... I found that with 4 turns of gap the velocity didn't increase below the setpoint, but it didn't fall off immediately either, giving me another 5 solid, usable shots below the setpoint.... the velocity didn't drop off until the pressure fell below 1800 psi.... What I had done was tune the gun to act like it was unregulated below the setpoint, with the velocity peaking about 100 psi below the setpoint.... but the curve is so flat at that point, the slight bump in velocity is lost in the SD.... The fact is, I have the gun tuned at 1950 psi, but I can use the tank down to 1800 and never even notice it.... all the shots stay within the normal ES, which is just over 1% (about 12 fps with unsorted pellets)..... The velocity with the 45 gr. pellets is just over 3% below the plateau, and with the 50 gr. pellets it is right at 4% down.... Once again, my preferred tune on a regulated PCP is right around 3-4% below the plateau.... I did one 7-shot mag. as an efficiency test with the 50.2 gr. pellets, and it worked out to 1.25 FPE/CI at an average of 916 fps (93.6 FPE).... This is not as good as yesterday, but the velocity is 30 fps higher, so pretty much expected.... I should still get about 35 shots at nearly 94 FPE with this tune.... and by using a 4500 psi bottle that would more than double....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on January 24, 2018, 04:33:12 PM
Here is what the .30 cal. looks like assembled....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/30%20cal%20BRod%20Wood%20ART-SS%20Valve_zpspnqmnbyh.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/30%20cal%20BRod%20Wood%20ART-SS%20Valve_zpspnqmnbyh.jpg.html)

It weighs 3 oz. more than the AR version.... The stock is heavier, but the barrel is lighter because of the CF sleeve to bring the diameter of the TJ's liner up to the same as the LW barrel (16mm).... all up with scope and rings it is 9 lbs. 11 oz.... I'm quite pleased with the appearance and ergonomics.... and it balances well, right where you would hold it near the front of the wooden stock....

Bob
Title: Re: Tale of Two BRods
Post by: Alan on January 24, 2018, 05:09:50 PM
Too bad you don't own Crosman/Benjamin!
Title: Re: Tale of Two BRods
Post by: Christopher on January 24, 2018, 05:46:31 PM
Too bad you don't own Crosman/Benjamin!

AMEN to that!!!

Great work Bob and excellent data sharing on the SS valve. Especially since I just ordered one.

Chris
Title: Re: Tale of Two BRods
Post by: rsterne on February 03, 2018, 11:34:38 AM
I spent the last 3 days casting bullets from all the moulds I got from NOE over the summer.... I went through about 20 lbs. of 40:1 lead:tin alloy from Rotometals, and cast bullets in .224, .243, .250 and .257 cal, and one in .308.... One of the bullets I cast was the heaviest BBT designed for .25 cal airgun barrels.... It turned out to be 58.3 gr. in that alloy for the FN version, and 55.0 gr. for the HP.... Here is what one looks like after pushing through the LW Polygonal barrel on my BRod....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/58%20gr%20250%20cal%20BBT_zpstclzsyla.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/58%20gr%20250%20cal%20BBT_zpstclzsyla.jpg.html)

The back of the nose measured 0.250" and the driving band 0.252" before pushing through.... After pushing through the choke, the driving band measured 0.251" across the grooves, and 0.246" across the "lands", but they did not drag on the center portion of the bullet, exactly the way it was designed to work.... At 1950 psi the HP just broke 800 fps, but I wanted to find out what it would do with the SS Valve at 3000 psi, so I swapped parts around to test that.... With the SSG adjusted for a turn of negative gap (preload) I got 952 fps with the FN (117 FPE) with a huge BRRAAAPPPP of air, but I assume that is the plateau velocity.... With a whisker of gap (less than 0.020") the report was normal, nice and crisp (although pretty loud) and I recorded 930 fps for the FN (112 FPE) and 950 fps for the HP (110 FPE).... Which is pretty good for the stock length LW barrel of just 23.8".... This gives a pretty good idea of what the SS valve is capable of.... The only way to get more would be to use a retracting bolt to provide unobstructed flow in the chamber, as right now it is the equivalent of 0.234", and I am actually using that for a transfer port diameter, as there is no sense in going larger....

This experiment gives significant insight into what could be done with the ART/SS Valve in .257 cal with a longer barrel, using a 4500 psi bottle regulated down to 3000 psi.... With a 28" barrel, 130-140 FPE should be quite possible, which would enable using the venerable Lyman 257420, which is the benchmark bullet in .257s.... My Hayabusa .257 (3000 psi fill, unregulated) with those specifications (with retracting bolt) reached a peak of 160 FPE, and can be tuned for a very nice string at over 130 FPE.... and that could be increased a bit if regulated to a solid 140 FPE.... There is no reason that the SS valve could not produce the same results, and be a LOT easier to cock as well.... My Hayabusa uses a 115 gram hammer, with a stroke of 1.2", and an 18 lb/in spring.... Cocking force at 160 FPE is 24 lbs....  :o

The experimenting I have done here provides a roadmap for anyone wishing to build a wonderful Varmint or long range target rifle, using proven components.... A 1/2" OD TJ's 25-20 barrel that is 28" long, with a 14" twist, the MRod action (modded for a retracting bolt), with an ART/SS Valve, and a 500 cc CF bottle regulated down to 3000 psi would supply the power.... Tensioning or sleeving the barrel to stiffen it, and maybe a harmonic tuner, should provide the accuracy.... Some decent optics, and an SCBA tank (for refills or tethering), and you would be good for a whole day of serious long-range Varmint busting....

Bob

Title: Re: Tale of Two BRods
Post by: sixshootertexan on February 03, 2018, 04:10:20 PM
Which .308 did you cast? Hope to see your test findings with it.
Title: Re: Tale of Two BRods
Post by: rsterne on February 03, 2018, 06:30:37 PM
It was the new 106 gr. straight sided NOE airgun bullet.... came out at 104 gr. FN and 98 gr. HP....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on February 04, 2018, 02:20:24 PM
Ran some test today with the .25 cal BRod tethered at 3000 psi.... still running the 12 lb/in spring with only 3 lbs. preload.... I was able to just reach the plateau at zero SSG gap as this pressure.... using my 47.5 gr. BBT HPs I got 1002 fps, and with the 50.4 gr. BBT FN I hit 977 fps (106-107 FPE).... At 3.5 turns of gap that dropped to 100 FPE with a nice crisp report.... I didn't check the efficiency.... but those HPs at 970 fps would sure lay a smackdown on anything up to Coyote size, I think....

Interestingly, this is very close to the same SSG setting I was using for the .30 cal BRod shooting 45-50 gr. pellets on 1950 psi.... and only a couple of turns less gap than the .25 cal shooting 34.1 gr. Kings on 1900 psi.... Once you find the sweet spot on the ART/SS valve it doesn't seem to require a lot of adjustment.... even with large changes of caliber or pressure....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on March 21, 2018, 12:18:54 PM
I have more information that would apply to someone building a 6 mm or .257 cal BRod, based on the results from this winter's PCP projects....

http://airgunguild.com/pcp-c02-and-helium-powered-airguns/any-interest-in-6mm/105/

The 6 mm with a 29" barrel, regulated at 2800 psi, is getting in the mid 900s with the 64 gr. bullet.... Since the Lyman 257420 is the same Sectional Density (0.155), this means that the idea I talked about above, using the SS valve in a regulated .257 BRod with a similar barrel length can be considered a proven concept using a 500 cc CF 4500 psi bottle.... Starting with a 1/2" OD TJ's barrel with a 14" twist, and sleeving it up to 5/8" with a CF tube inserted into the front of the receiver just shy of the 4-40 screws is completely feasible, although you would have to single load bullets of that length (maybe)....

This brings up a new idea I am working on for longer magazines to fit the MRod receiver, for up to .357 cal.... There are several ways to do this, and here is the first prototype I am working on....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Machining%20Magazine_zpsyf9ab0xu.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Machining%20Magazine_zpsyf9ab0xu.jpg.html)

The magazine is shown mounted in a 5C collet in a hex block to enable indexing to drill the holes for the pellet/bullets.... You can see a JSB .35 cal pellet on the right, and a 154 gr. .357 cal bullet on the left (they are sitting on a couple of pieces of dowel to raise them up for the photo).... The material is a piece of 1.25" OD 2024-T3 aluminum bar stock, and it is long enough to make 2 mags.... I am not sure yet how I will mount the mag. and it will likely have to be indexed manually, but one way it could be mounted is on a retractable pin set into the MRod receiver, similar to the way a Hatsan mag. is located.... I checked the width of the mag. slot in a .25 cal MRod receiver, and it is long enough to accommodate that 154 gr. bullet if there is nothing else in the slot, and the barrel is not protruding.... This isn't my plan, I would never want to shoot anything that heavy.... and likely I will make the mag. wheel thinner to help mount and index it.... but it does shown some possibilities....

The other way to make a mag. for a .357 cal. is to copy the MRod .25 cal mag. but with a larger wheel in a similar housing, possibly made by a 3D Printer.... I have drawn one up and sent it to Travis for him to look at.... It would be the same inside length (0.45") as the .25 and .30 cal mags, but that would fit the JSB 81 gr. pellets, the EPP-UGs, and my 109 gr. BBT.... so likely all the length you would need for most .357s based on an MRod.... The advantage to this method is that it would be self-indexing....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on March 21, 2018, 07:01:00 PM
Well I got sidetracked on the long .357 aluminum mag project.... I had another look at the .25 cal MRod mag. and came up with a different way to modify it for .35 cal and still use the original housing, albeit modified somewhat.... The first step was to make a .35 cal wheel that would fit inside the .25 cal mag. and the only way to do that was to reduce the radius that the holes are on that hold the pellets from 0.50" to 0.45".... This would normally raise the center of the pellet 0.050" above the boreline, but I realized that if I inserted the magazine further to the left, while keeping the feed hole at the same height (which it must be to align the pellet with the bore), I could just rotate the wheel a bit more counter-clockwise (when viewed from the back) to get the height to work out.... here are some photos of the work so far....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Wheel%20for%2035%20cal_zps2bzp0flp.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Wheel%20for%2035%20cal_zps2bzp0flp.jpg.html)

The wheel was machined from a piece of MDS, with seven positions, one of which uses a glued in blanking plug that prevents you from closing the bolt when the mag. is in the empty position.... Drilling 7 holes was a challenge with a manual milling setup, the key was to use an online calculator to convert from Polar coordinates (radius and angle) to Cartesian (x and y) coordinates, and then just position the vertical and crossfeeds on the milling attachment on my lathe to drill the 7 holes around the 0.9" diameter circle.... It worked out great, although there was a lot of hand finishing to do, removing the milling flash where the holes broke through the outer diameter of the wheel.... You will notice that the recess in the back of the wheel for the torsion spring is smaller in diameter, so I will need to find or make a smaller OD spring to force the necessary rotation of the wheel to make the mag. self-index....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/25%20cal%20with%2035%20cal%20Wheel_zpscjuvn1dg.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/25%20cal%20with%2035%20cal%20Wheel_zpscjuvn1dg.jpg.html)

Here is a photo with the wheel in place, but I have not yet moved the feed hole over in the outer casing, or milled away part of the bump stop to make it stop in the correct place.... In the photo below I have machined a larger hole in the clear cover in the correct location.... You can see that it is shifted about 0.090" to the right of the original location.... and you will notice that part of the bump stop will have to be machined away when I mill the hole in the outer housing in the correct location to allow the mag. to slide to the left....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Cover%20Hole_zps2fval8wi.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Cover%20Hole_zps2fval8wi.jpg.html)

There are lots of things that will remain to be done to make the mag. functional.... the spring as I mentioned, and a new location for the small brass pin that rotates the wheel to allow loading pellets when you rotate the cover.... I will also have to figure out a way to hold the mag. in place, because the slot in the front for the barrel will lose the little bumps that allow the mag. to "snap" into place on the barrel stub.... First I have to get the mag. to function and line up.... then I will worry about the details....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on March 22, 2018, 03:51:15 PM
I took me many hours and lots of hand work, but I now have a fully functional 6-shot .35 cal MRod magazine, made from a .25 cal.... Here are the photos....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Spring%20and%20Wheel_zpswxb2tw3d.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Spring%20and%20Wheel_zpswxb2tw3d.jpg.html)

The spring is a mess, cosmetically, but it works.... I made it by winding the stock spring around a 9/32" drill bit to tighten the coil enough to fit inside the 1/2" hole in the wheel.... Of course it came out a mess, so I spent a lot of time with two needle-nose pliers tweaking it to get it to work....  ::) .... I had to hand carve the groove for the pin in the cover that rotates the wheel with a tiny burr on a Dremel, and again it may not be pretty but it is functional....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Housing%20and%20Wheel_zps8odtugcl.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Housing%20and%20Wheel_zps8odtugcl.jpg.html)

The housing was milled out with a 3/8" end mill to move the hole over and increase it in size.... There is a 1/32" hole drilled through the filler plug in the wheel for the tail of the spring, which is installed in the photo....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Magazine%20Front_zpsyxqetb4o.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Magazine%20Front_zpsyxqetb4o.jpg.html)

The position of the feed hole, and it's associated recess that clips over the end of the barrel were the key to this project.... They are the same height as in the stock .25 cal magazine, but are moved 0.084" towards the centerline of the mag..... That was necessary for the hole to line up with the smaller radius of the wheel, which was necessary so that the pellets fit inside the housing.... I was concerned about how to retain the magazine in the slot, but as it turns out, that was a non-issue.... When I plunged the 1/2" mill into the front of the housing to create the recess, it left two tiny bumps that slide past the barrel when you insert it, exactly the same as on a stock mag.... The difference is that as you slide the mag. into place, you feel it "click" twice as it slides past the OD of the barrel, once for the stock bumps, and then for the new ones, which are actually tighter than original.... Once in place, the mag. protrudes that 0.084" past the left hand side of the receiver because it sits that much further to the left to line up....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Full%20Magazine_zps9rib7dsb.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Full%20Magazine_zps9rib7dsb.jpg.html)

Here is a photo of the loaded magazine.... You can see the brass rotating pin, which I had to relocate, and the enlarged, kidney-shaped loading slot in the clear cover.... It functions perfectly, indexing to the next pellet each time you push one out.... I even tried it sitting on the end of my .357 barrel, and the pellet just slides right into the bore, exactly as it should.... Now that I have figured out how to do this, I will order another .25 cal MRod receiver and bolt, and a PRod trigger group and AR stock so that I can complete a third BRod in .357 cal.... I already have the bottle, tank block, and a spare FLEX tube, and most of the parts to make a valve.... so it looks like a regulated .357 BRod repeater shooting pellets is the next project.... although it likely won't get done until next winter, I am quickly running out of time as spring is here and the Motel will soon be busy....

Bob
Title: Re: Tale of Two BRods
Post by: Monkeydad1969 on March 25, 2018, 08:46:16 AM
Nice work, Bob.

Joe
Title: Re: Tale of Two BRods
Post by: rsterne on March 25, 2018, 09:54:23 AM
Now that I have proved it can be done.... some enterprising guy (like Lloyd did with his .30 cal conversion) could make new wheels, fit them with the appropriate spring, remachine the housing and cover plate (or make a new cover plate) and supply a .35 cal conversion mag. for the MRods.... It won't take a very long bullet, but I think will cover all the weights necessary for a modified MRod.... It will accept the JSB pellets, the EPP-UG, or my 109 gr. BBT, and likely a few others.... If a new cover plate was made with a groove machined in it, and/or the groove in the front of the housing widened, slightly longer bullets could be accommodated....

Certainly it would serve the purpose of having a .35 cal MRod repeater.... It would be a good idea to upgrade the bolt locking lug to stand the much increased force on the bolt from the larger bore.... but that can be done by going to a 10-32 from the stock 8-32....

Bob
Title: Re: Tale of Two BRods
Post by: rsterne on June 28, 2018, 12:24:33 PM
I cast up the new NOE pellets today.... The mould comes with 4 sets of RG base pins, and they produce 3 skirted pellets and one solid with a flat base.... They look like this....

(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/NOE%2030%20cal%20Pellets_zps6857okt2.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/NOE%2030%20cal%20Pellets_zps6857okt2.jpg.html)

The weights in 40:1 lead/tin alloy are 35.0, 37.0, 38.5 and 42.6 gr.... They all chamber perfectly in my .25 cal LW Polygonal barrel, but that is not surprising as I cut the chamber to allow for bullets as well as pellets.... I have my BRod set up with a Cothran valve and the WAR adjustable regulated tank block, set at 1900 psi.... I checked the velocity of all 5 pellets (including the JSBs) and got the following averages for one 8-shot magazine of each....

34.1 gr. JSB = 947 fps (67.9 FPE)
35.0 gr. NOE = 937 fps (68.3 FPE)
37.0 gr. NOE = 919 fps (69.4 FPE)
38.5 gr. NOE = 906 fps (70.2 FPE)
42.6 gr. NOE = 871 fps (71.8 FPE)

I was only shooting inside my shop, with the backstop 20 feet away, and all groups were one ragged hole, with no real difference between any of the pellets.... That is encouraging, because some pellets or bullets can't do that when shooting through the Chrony at that distance.... and those that do usually shoot pretty good at least out to 50 yards....

My summer is taken up with sitting at the Motel reception desk waiting for guests, and we are entering our busiest season now, so it is unlikely I will get to try these at distance any time soon.... but the velocity and energy is right where I want it for testing.... I can't wait....

Bob
Title: Re: Tale of Two BRods
Post by: Monkeydad1969 on June 29, 2018, 05:17:15 AM
They look good Bob.  Hopefully you'll possibly get a lull in the action at the front desk. Lol

Joe
Title: Re: Tale of Two BRods
Post by: rsterne on July 03, 2018, 03:02:06 PM
My parts came in today from Joe at DiscosRUs, and I didn't waste any time whacking the front off the Gen2 MRod stock and grinding it out to fit over the WAR tank block.... Here is what it looks like with the Gen2 trigger installed also, plus a 500 cc 3000 psi aluminum bottle....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/BRod%20Gen2%20Stock_zpseu5dsmi0.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/BRod%20Gen2%20Stock_zpseu5dsmi0.jpg.html)

I left the stock long enough to cover the tank block and the bonnet section of the regulator.... There is a bulkhead in the stock JUST in front of the front of the tank block when it is mounted in a WAR tube, so about 3/4" ahead of that is where I made the initial cut, and then ground it to fit with my Dremel....

I also purchased a .25 cal MRod receiver and bolt, which I will be modifying as before to fit the .357 cal TJ's 26" twist barrel I have, with a high-modulas CF sleeve glued over it to stiffen it, like I did with the .30 cal barrel.... I already have a modified .25 cal MRod magazine which will give me a 6-shot .357 cal repeater when it is all together.... I probably won't get much done before the winter, but at least I now have all the parts, other than the valve and hammer which I have to make....

Bob
Title: Re: Tale of Two BRods
Post by: Monkeydad1969 on July 03, 2018, 03:29:39 PM
Keep it coming, Bob.  Looking good.

Joe
Title: Re: Tale of Two BRods
Post by: rsterne on November 18, 2018, 03:32:38 PM
Well, the Motel busy season is over for another year, and it's time to hit the shop again.... As promised, the first order of business is to do a .357 version of my BRods…. The parts have been sitting on my bench gathering dust since the Spring.... it's been so long I had to sit down and think about where to start....  ::)

I decided to bore out the receiver for the 0.640" OD Hi-Mod Carbon tubing I used for the sleeve on the .30 cal TJ's barrel, as the .357 liner I have is the same 1/2" OD.... I had a hard time trying to drill it straight, for some reason this receiver just didn't want to run straight in my 4-jaw chuck.... so I drilled it undersize and then held it in my milling attachment, set it up with the bore of the receiver parallel to the ways and lathe C/L, and then used a 5/8" end mill to straighten the hole and move it over so that it lined up with the original 1/2" bore of the receiver.... It took a lot of fiddling, but the result was great, the outer sleeve and the barrel liner both slide into place perfectly.... The counterbored hole for the sleeve is 1.400" deep, so it stops just short of the 4-40 screw holes in the front of the receiver....

I then mounted the receiver across the lathe, in the milling attachment, and centered off the transfer port hole, drilled it out to 9/32" (0.281"), and counterbored it 3/8" x 0.150" deep for the transfer port.... That leaves 0.100" of receiver below the barrel, so the Teflon transfer port will seal against that shoulder with a slight amount of compression against that and the valve.... Travis assures me that you don't need to seal the transfer port against the actual barrel, that the set screw in the receiver that is directly above the barrel port pushes the barrel down against the receiver tight enough to seal OK.... I sure hope he's right about that, as there really isn't enough barrel wall to mill a 3/8" OD flat without hitting the bore.... A .357 barrel with a 1/2" OD only has a 0.070" wall thickness, which is one of the reasons for using the High Modulas CF tubing, to get the greatest stiffness possible for the barrel.... Here is what the receiver looks like at the moment....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20BRod%20Receiver_zpsyorxcggy.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20BRod%20Receiver_zpsyorxcggy.jpg.html)

The Teflon transfer port will be 3/8" OD x 9/32" ID.... I chose that port diameter because it is 79% of the caliber, which means I don't have to mill an oblong barrel port, I can just drill it.... It should be plenty big for a pellet shooter, IMO.... The plan is to build my own SS valve, with a matching exhaust port, and I'm going to try for a 0.323" throat on the valve (a size "P" drill), which with a 1/8" stem will give be about 12% more throat area than port area.... Using a 3/8" OD PEEK poppet I will have a 0.026" seat margin, which should work OK.... That will allow me to build the same "guts" for this valve as I did for my 6 mm and .257 valves last winter.... which will reduce the development time....

I'm looking forward to progressing on this build as time permits.... It certainly feels good to get back in the shop again.... It's been a loonnngggg summer.... ::)

Bob
Title: Re: Tale of Two BRods
Post by: Motorhead on November 18, 2018, 10:15:23 PM
Bob,
good to hear your back in the "Cold" shop once again .... watching this build progress  8)
Title: Re: Tale of Two BRods
Post by: rsterne on November 19, 2018, 04:59:19 PM
Two shop days in a row!.... WOO HOO !!!

Today I modified the .25 cal MRod bolt for this .357 cal build.... Two things had to change, the diameter of the bolt and probe, and the size of the lockup pin.... Crosman use an 8-32 SHCS for the bolt lockup in the .25 cal, and at the same pressure the .357 bolt will have twice the load on it.... Through the threads (the weakest point), a 10-32 has about 50% more shear strength of an 8-32, and I will be using only about 2200 psi instead of 3000, so that is what I used.... The bolt is hardened, so I had to heat it to cherry red and let it cool slowly to anneal it.... Once annealed, I could drill and tap the hole out to 10-32 and mill a 1/4" flat for the head to tighten against, and I made a new locking pin from a 1/2" long SHCS with a nut screwed tight against the head to lengthen it.... I turned the head and nut down to 1/4" OD, and shortened it slightly so that it doesn't rub on the tube when the receiver is installed....

To make the larger probe, I used a piece of 3/8" CRS, and drilled it 1/4" to a depth of 3/4" and then shortened the stub of the bolt so that it just slid in full depth.... The OD of the new bolt nose was turned down to 0.356", and I made a longer probe that is 0.125" diameter (which just fits inside a JSB pellet) of the correct length to load the back of the skirt just ahead of the barrel port.... The shoulder between the two diameters I made a 20 deg. taper, which I figured won't restrict the flow, and will slightly reduce the chamber volume behind the pellet.... After taking the photo below of the parts, I installed the new bolt nose with permanent Loctite 638 (green)….

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Bolt%20Parts_zpsf83gzbcv.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Bolt%20Parts_zpsf83gzbcv.jpg.html)

The cocking slot in the receiver needed to be widened a bit for the larger pin, and because I use an 8-32 SHCS as my hammer pin.... The front of the slot on the left side also needed machining wider and deeper, to allow the bigger lock pin to properly lock up the bolt.... You can see those mods in the photo below....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Receiver%20Slot_zpsdgrmtkrr.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Receiver%20Slot_zpsdgrmtkrr.jpg.html)

The other job I did today was to shorten the barrel and ream a new chamber.... The barrel was previously used in another receiver, but the barrel port position would not work for this build.... I already had a chamber reamer, so all I had to do was stone the cutting edge with a fine grit diamond file and cut the chamber deeper.... I left the barrel in the lathe because tomorrow I will cut the O-ring groove to seal the bolt before removing it from the chuck.... The photo below shows the completed .357 cal MRod bolt, the chamber reamer, and the tool I will use to cut the groove for the 1 mm x 9 mm O-ring....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Bolt%20and%20Special%20Tools_zpsxhcbavae.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Bolt%20and%20Special%20Tools_zpsxhcbavae.jpg.html)

With a little luck, I will have the machining done on the barrel tomorrow, including the new barrel port, and be ready to glue on the carbon fibre sleeve....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 20, 2018, 08:27:36 PM
Today I finished off the barrel by machining the O-ring groove, drilling the barrel port, and gluing on the CF sleeve.... Here is what the breech end looks like now....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Barrel%20Port%20O-ring%20Groove%20and%20Sleeve_zpsej9yvnp7.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Barrel%20Port%20O-ring%20Groove%20and%20Sleeve_zpsej9yvnp7.jpg.html)

That 9/32" barrel port is pretty huge, and you can see how thin the barrel wall is with a 1/2" OD and a .357 bore.... I had to sand the outside of the CF sleeve slightly to get a nice slide fit inside the receiver, it was just a bit too snug.... There isn't a lot of room between the barrel port and the back of the barrel, another reason I had to use a tiny 1 mm CS O-ring for the breech seal.... I tried the bolt with the barrel installed in the receiver, and it slides into battery perfectly.... It loads a 78 gr. JSB pellet (which has a slightly deeper base cavity than the current 81 gr. version) nicely past the front of the barrel port.... It should also work perfectly with the new NOE Magnum Hunter pellet with the medium base pin (86 gr.).... The skirt of an 81 gr. EunJin pellet does not quite load past the front of the barrel port, so neither would the 81 gr. version of the NOE pellet which uses the deepest base pin.... I could not use a longer loading probe or it would not retract far enough to clear the mag. well.... This .357 build is really pushing the limits of an MRod receiver, the tolerances are virtually non-existent....

Before assembly with the Loctite 638 I sanded the outside of the barrel and the inside of the carbon tube with 100 grit to give them both some "tooth".... I had a nice slide fit, the barrel fell through the sleeve under its own weight.... Tomorrow, after the initial 24 hr. cure at room temperature, I will give the Loctite a post cure at 175*F for 3 hours.... Loctite is designed primarily for gluing metal, and this post cure makes a huge difference in the bond strength to a non-metallic sleeve.... Cured 638 has a shear strength of 4500 psi, which rivals the best epoxies.... While the barrel is curing I plan to make the new rear tube plug and SSG....

Bob

Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Alan on November 21, 2018, 04:50:03 AM
No photo!
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 21, 2018, 08:41:47 AM
Photobucket was having problems yesterday, I had to wait to upload the photo.... It is working for me, and probably will for you the next time you look....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 21, 2018, 04:26:39 PM
This afternoon I finished fitting the barrel to the receiver, adjusting the length of the back of the sleeve to stop the barrel in the correct place for the magazine to fit properly.... I use a 1/2" ID O-ring slid over the barrel against the end of the CF sleeve to provide a bit of resistance, so that I have to push it hard into the receiver to seat it, compressing the O-ring.... It will also seal the barrel to the receiver, should there be any slight leak between the barrel port and receiver port.... That won't help much, as any leak will be directed back towards the magazine, but it can't hurt.... I drilled a hole through the carbon fibre sleeve so that the front setscrew tightens against the steel barrel liner.... After fitting the barrel I fed one pellet from my modified MRod magazine into the barrel, and it worked perfectly.... You could feel a bit of resistance the last 1/8" as the pellet engaged the rifling.... Here is what the pellet looked like when pushed back out through the breech....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/78%20gr%20JSB_zps8fcgppun.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/78%20gr%20JSB_zps8fcgppun.jpg.html)

You can see that the head of the pellet nicely engraves from the lands, but the skirt stops in the parallel portion of the chamber, as intended.... The next job was to make a new rear plug for the tube to hold the SSG I will be making.... This was an exact copy of the one I made for the .30 cal.... Here is a photo.... The bottom grooves are air vents to prevent any vacuum building up behind the hammer on firing....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Rear%20Plug_zps82i1pzhq.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Rear%20Plug_zps82i1pzhq.jpg.html)

Tonight, after dinner, I will post cure the Loctite 638, and tomorrow I should be ready to install the barrel in the receiver.... That will complete the work on the .357 upper.... I still have to make a new SS valve, hammer and SSG for this build.... but I am very pleased with the progress so far....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 22, 2018, 03:43:26 PM
I installed the barrel in the receiver today, and then made a transfer port with a 9/32" ID from a short piece of 3/8" Teflon rod.... I made it to fit the .30 cal lower and accept the .357 cal upper, just for testing purposes.... It sealed up perfectly, and I am delighted to say that Travis was right, it didn't need to seal to the barrel, just between the receiver and valve.... The pressure of the setscrew in the MRod receiver directly over the barrel port presses it down hard enough against the receiver that it doesn't leak when firing, even at 2900 psi.... The valve in the .30 cal lower is an ART-SS Valve with a 0.257" exhaust port, one of the early ones with the 1/4" small end on the poppet, and I am running it with the stock inlet jet, which I believe is a #87.5, or about 0.035".... I have a 51 gr. MDS hammer in place, and the SSG is equipped with an 8 lb/in. spring, with 0.37" of preload (3 lbs)…. Here is what the .30 cal BRod looks like with the .35 cal upper in place....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/35%20BRod%20Temporary_zps5zryxt6n.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/35%20BRod%20Temporary_zps5zryxt6n.jpg.html)

I tethered the gun at both 1900 psi and 2900 psi, and tested 3 different pellets, all of nearly the same weight, a 77.5 gr. EunJin, the 78.0 gr. JSB (no longer made) and the newer 81.0 gr. JSBs.... At 2900 psi I also tested a 119 gr. BBT-HP and a Lee 154 gr. RF.... The EunJins were indistinguishable from the 78 gr. JSBs, so they are not graphed in the chart below.... The dotted lines are at 1900 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/35%20BRod%20ART_SS%20Valve_zpskqhflguz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/35%20BRod%20ART_SS%20Valve_zpskqhflguz.jpg.html)

At 1900 psi the velocity is nearly maxed out with a slight gap in the SSG (shown as "0"), so the hammer and spring combination is usable as is.... At 2900 psi the velocity increases somewhat with preload on the spring.... With negative 2 turns of gap (about 4 lbs. of preload on the valve stem) the velocity increases 5% with the pellets and about 10% with the bullets.... so either more spring preload on the SSG or a heavier hammer spring would be necessary to allow proper tuning at that pressure.... Since this is just a preliminary test, with a valve I won't be using, I didn't bother making either change, but it shows what the FPE is that is available with a valve with 1/4" porting and a plenum volume of about 85 cc.... With these results, I feel that the plenum is a bit too small for a .35 cal, there is simply too much barrel volume relative to the plenum volume, and this is limiting the FPE.... On this .357 cal, the plenum volume is less than twice the barrel volume.... On the .30 cal it is nearly 3 times the barrel volume, and in .25 cal it is over 4 times the barrel volume....

I got the following results, testing with this valve....

At 1900 psi
77.5 gr. to 81.0 gr. pellets = 131 FPE Maximum.... 125 FPE with a slight SSG gap

At 2900 psi
77.5 gr. to 78.0 gr. pellets = 173 FPE Maximum.... 158 FPE with a slight SSG gap
81.0 gr. pellets = 176 FPE Maximum.... 162 FPE with a slight SSG gap
119 gr. BBT-HP = 191 FPE Maximum.... 161 FPE with a slight SSG gap
154 gr. Lee RF = 194 FPE Maximum....

As a comparison, I previously used this barrel (though 1" longer) on my Disco Double, running a Cothran valve at 2900 psi.... The Disco Double, however, has a 135 cc plenum.... Here were the results tethered at 2900 psi....

78.0 gr. JSBs = 172 FPE.... and at 1900 psi = 132 FPE
127 gr. BBT-FN = 206 FPE
154 gr. Lee RF = 219 FPE

As you can see, the results with pellets are virtually identical.... However, with bullets, the Cothran valve was able to produce a bit more FPE, but that is probably due to the 60% larger plenum volume.... I am hoping that when I make a new SS valve with a larger throat and ports I can pick up a bit more FPE.... However, that 85 cc Plenum will continue to be a limiting factor to the FPE....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 23, 2018, 03:53:33 PM
Today I started working on an SS Valve for the .357 BRod…. I couldn't start with an MRod valve unless I wanted to add a longer seat, because the 9/32" port I want would destroy the valve seat, as there simply isn't enough material there.... I looked in my box of used parts, and I found a scratch built valve body that Travis had sent to me where the seat had been moved forward and the port was on an angle.... The threads in the front of the valve were damaged, but I didn't need those, and after some careful measuring I decided I could probably modify it to work....

The ID of the tube I have is a fraction smaller than an MRod tube, so I had to turn down the OD of the valve a few thou to fit.... I then drilled the front of the valve out to 5/8" ID back to just in front of the 4-40 screw holes.... The hole through between those was already just over 1/2", and you can't go to 5/8", it would break through into the threaded holes and the valve would leak.... That 1/2" hole went right back to the valve seat, but I wanted more flow inside the valve, because the thimble of the SS valve will be 7/16" OD.... So, I bored out the back part of the valve ID to 5/8", using an internal threading tool with a 60 deg. point.... Again, I stopped just behind where the 4-40 holes were, but the part behind them, back to the seat, was now 5/8" like the front....

The middle of the valve was still 1/2" ID, however, so I put the valve in the milling attachment on my lathe, and set it up with the 4-40 holes vertical.... I ran a 1/2" end mill down inside the valve and centered it in the hole, and clamped the crossfeed down.... Now, by using the vertical travel on the vice, I could change the round hole into a vertical slot, that was 1/2" wide and 5/8" tall.... This worked perfectly, and now the inside of the valve is 5/8", except for a couple of small bumps on the sides where the 4-40 screws are....

I then drilled the throat of the valve out to a size "P" drill, which is 0.323", and touched up the valve seat by hand with a 1/2" end mill to make sure it was square to the bore.... I then turned a 3/4" ID recess in the front of the valve to a depth of 0.30", to locate the perforated mounting "wheel" which will hold the front of the SS valve thimble.... The last step inside the valve was to machine a snap ring groove to hold that wheel in place.... I tried a thimble, and there is tons of room around it for flow....Here is what the inside of the valve looks like now....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Valve%20Inside_zpsbxyg2pbw.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Valve%20Inside_zpsbxyg2pbw.jpg.html)

I had to enlarge the port from the 7/32" it was to 9/32".... I centered off the existing port, which was on a 20 deg. angle, and enlarged the hole to 1/4" with an end mill.... It was getting pretty close to the seat, and I still had to go larger, to 9/32, so I reduced the angle to 15 deg. and used a 17/64" end mill to enlarge the port.... That left the top of the port nearly 9/32" fore and aft (because of the angle), so I offset the mill 0.010" higher and lower to make the port oval, but because of the angle it appears round.... I then enlarged the recess for the transfer port from 5/16" to 3/8".... The rest of the port work was done with a Dremel, smoothing the transition of the exhaust port into the throat, and making sure the port was a full 9/32" everywhere.... By the time I was done, I could slide the shank of a 9/32" drill into the port all the way to the throat.... Here is what this huge port looks like.... It is 4 times the area of a .25 cal MRod port....  :o

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Valve%20Port_zpsbw1gx0q5.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Valve%20Port_zpsbw1gx0q5.jpg.html)

This valve was made for a Gen1 trigger, and I am using a Gen2 for this build, so I had to mill two more shallow pockets in the bottom to clear the screws.... I had a poppet for an SS valve I built for my 6 mm left over, so I used it to lap the seat, and it looks like it should seal OK.... Tomorrow I plan to make the mounting wheel for the front of the valve, and using the poppet and thimble I have see if I can get it to seal up.... If so, testing should follow shortly.... For now I will use a 105 gr. steel hammer I have left over from the start of the BRod project, before I tried the Cothran and SS Valves.... It may be too heavy, but it will give me a starting point, and I can always borrow the 51 gr. MDS hammer currently in the .30 cal for testing....My gut feel is that I may need something in between, but that will depend on how easy this SS valve opens....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 24, 2018, 06:09:30 PM
I worked on the inside of the valve today.... I had a poppet and thimble from the first SS valve I made, using the dimensions Lloyd used on his prototype.... The small end of the poppet is VERY hard to machine without breaking it in Delrin, so this one had a brass body with a Delrin overlay.... I have since changed the dimensions, which Travis did too.... in my case to make it easier to machine.... Here is a photo of the parts.... Note the air passage ground into the shaft which vents the area between the O-rings to the exhaust port, that is key to its operation....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20SS%20Valve%20Thimble%20and%20Poppet_zpsfwyaryct.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20SS%20Valve%20Thimble%20and%20Poppet_zpsfwyaryct.jpg.html)

Last year I avoided showing any photos of the inside of my SS copy, to protect Travis' investment.... but there have been a few photos posted, and I think most people know what it looks like inside, so I figured there would be no problem sharing what I made myself.... In addition, Travis gave me permission to make a generic drawing of an SS valve to include in the next article I am writing for HAM on balanced valves, thanks Travis.... Here is the completed SS valve.... The valve stem is short enough that the hammer cannot drive the poppet to the end of its travel, which could damage it.... I still have 0.200" of travel....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20SS%20Valve%20Complete_zpsb7hcivgs.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20SS%20Valve%20Complete_zpsb7hcivgs.jpg.html)

Here is a photo of the front end, showing how the thimble is mounted, secured by the snap ring.... The way I build the wheel allows a small amount of radial movement for the thimble, so that it can self align with the poppet....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20SS%20Valve%20Front_zpsjndczq3k.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20SS%20Valve%20Front_zpsjndczq3k.jpg.html)

Note the vent hole in the mounting screw.... This allows HPA to enter the front of the thimble, in front of the small O-ring.... The spring only needs to be strong enough to overcome the friction of the O-rings and seal up the valve for initial filling.... Travis uses adjustable jets instead of my fixed 1/16" vent hole, to allow for fine tuning....

Unfortunately, this version didn't work.... The Delrin part of the poppet came loose on the brass rod.... I had another poppet, with a larger front end, that I had made for my 6 mm, but I didn't have a thimble for it.... I made a new thimble, and reassembled the valve.... It STILL leaked.... By this time I was tearing out what little hair I have left....  ::) …. I tried lapping the seat, replacing the O-rings, I even turned the poppet sealing face to re-true it, but the leak got worse and worse, lots of air coming out the exhaust port.... I eventually figured a way to test the O-rings on the poppet, and there was no air leaking out the back of the thimble or through the vent hole, so the only place left was the seat of the valve.... I spun the poppet with a drill to leave a polished ring on the seat, and it was off center, relative to the valve throat.... When I drilled out the throat I guess the drill tended to follow the exhaust port and ended up off center.... Since the sealing margin is so small (0.323" throat and 0.375" poppet) I guess there isn't enough seat on the side nearest the exhaust port, and that must be where it is leaking....  >:(

This is about the hardest thing to fix, unfortunately.... I can either make an entire new valve body, or try to repair the one I have.... Since I have a lot of hours into this one, I'm going to try and fix it.... Tomorrow I plan to make an insert for the back of the valve, with a new throat, seat, exhaust port and valve stem guide hole, and try and get it all straight and centered.... Then I will have to machine out the back of the valve body to install it.... There are a couple of different ways to do this job, I'll be pondering that overnight....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Gerard on November 24, 2018, 07:00:02 PM
Dang, that's too bad. So it goes sometimes when working things out. When I build stuff it's usually designing on the fly - seems I have a mild allergy to drawings and pre-thinking plans, just prefer to do a step, think about the new problems I've generated, solve those and continue. But yeah, sometimes a procedural error like introducing an asymmetric hole before drilling another is just something really hard to resolve. Carbide milling bit to re-bore maybe, then make a bigger poppet? Maybe that's nonsense. But stiff boring tools can sometimes sort out off-axis issues.
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 24, 2018, 08:28:02 PM
I am contemplating a slightly larger poppet, possibly made of PEEK.... big enough to cover the off-center throat....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 25, 2018, 06:37:08 PM
Well I wasted all morning trying everything I could think of to get this thing to stop leaking.... I finally decided to bore out the back of the valve and replace the seat and valve stem hole with an insert.... When I started boring out the back of the valve I heard a strange scraping noise, and found out why it has been leaking all this time.... Travis must have made a seat insert to move the seat forward, because my end mill caught it and spun it around in the valve body.... I pushed it out, and this is what I found....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Valve%20Seat%20Insert_zpspymkswzu.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Valve%20Seat%20Insert_zpspymkswzu.jpg.html)

So the air leak I had tracked down to the poppet on the seat was not the problem at all.... The air was leaking around the sides of this insert and then escaping out the exhaust port.... It may not have leaked when Travis installed it, but by the time I hogged out the ports, there was obviously a crack opening up between the OD of the insert and the ID of the valve body.... ARRGGGHHHH!!!!!....

Anyways, I used a 9/16" end mill, working from the back of the valve, to mill out the inside all the way to (and removing) the seat.... I then had to make an insert, sealed by 2 O-rings, and retained by the three valve screws and a setscrew in the top.... It looks like this.... The insert is upside down, relative to the valve in this photo, so you can see the throat and port better....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Valve%20Insert_zpsmhin6noz.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Valve%20Insert_zpsmhin6noz.jpg.html)

There was hardly any room between the seat and the front of the port, so I had to use a thin Metric O-ring and stretch it into place in a narrow and shallow groove.... I hope there is enough material between the groove and the port that it doesn't fail.... There is quite a bit of load on this part (510 lbs. at 2000 psi) so after I installed a setscrew in the top I drilled down and tapped the three valve screws to retain it.... It isn't going anywhere....  ;)

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20Insert_zpszm4hdslf.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20Insert_zpszm4hdslf.jpg.html)

If you look closely, you will see a thin, shiny ring around the throat of the valve.... I spun the poppet around with a drill to lightly polish the seat, and make sure it was centered and had a wide enough overlap.... I don't think there should be any further problem getting this valve to seal, although sliding the insert into the valve body without slicing that tiny front O-ring may be a challenge....  ::)

I've had enough frustration for one day.... Tomorrow I will find out if I finally got this valve to seal up....  ???

Bob

Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Nicesurprice on November 26, 2018, 02:38:05 AM
Nice project.
And it never comes easy
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Alan on November 26, 2018, 04:31:11 AM
Through adversity, comes knowledge.
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Gerard on November 26, 2018, 08:11:14 AM
If I'd run into that horrid little spinning piece after putting in all that work, I suspect my solution might have been to tap the hole, make a matching threaded aluminum rod section, and bond it into place with some slow curing JB Weld. I'm almost certain I'm missing something about how this fits together else I'd not be saying that... but adding two O-rings would, for me at least, make for two potential leak points too many. And at least one of them would probably leak right away. Steel-filled JB Weld is rated for some fairly high pressure with just clean metal on metal. Applied to a threaded insert it's likely about as strong as the original solid piece of aluminum. After curing s while that is.
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 26, 2018, 09:03:58 AM
Gerard, your solution seems logical.... if I hadn't tried that previously on a valve and ended up with a leak that (like this time) took me FOREVER to find.... The JB Weld cracked just enough for the air to find its way out.... a pinhole, and a slow leak.... but happened nevertheless....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Gerard on November 26, 2018, 09:40:51 AM
Ah well, there you go. It'd be a rare thing in machining airgun parts that you hadn't tried already. Shame that attempt failed. I've only used steel filled JB Weld once against a high pressure leak - a valve in the plenum volume of my son's 2240 carbine which just would not seal owing to the mess of going through both the main steel tube and into a rather small gauge block. Next time (if I were to do that one again) I'd make an offset hole so as to facilitate longer threaded contact between gauge block and gauge threads. Putting two O-rings at each end of the block, in grooves separated by about 1mm, didn't fix the slow leak so it had to be the threads... and sure enough, melting some beeswax onto the gauge threads then threading that into some JB Weld made it capable of holding pumped pressure for months at a time. But one success does not a proof make. Got lucky. Speaking of which, best of luck with this continued adventure.
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 26, 2018, 03:36:50 PM
I also glued in a pipe plug with JB Weld in a tank block once where I tapped it too deep, and if I screwed the plug in, it would have hit something critical inside.... So I cleaned the plug and hole with acetone, blew it out with compressed air, coated both the plug and tapped hole with JB weld, screwed it in to the required depth, and let it set overnight.... Believe it or not the HPA found a trail along the spiral of the threads and I had a slow leak.... I've given up on JB weld as a HPA sealant, after these two experiences....  ::)

I assembled the valve very carefully today, making sure I didn't damage the small front O-ring on assembly, and I'm please to say there was no leak between the new insert in back end of the valve and the valve body.... I had to disassemble one more time to lap the poppet to the new seat on the insert, and I'm please to say that I now have NO leaks.... Having assembled the tube successfully, I decided to put the rest of the gun together and test it.... I ran into one slight problem, the Gen2 trigger sear was a fraction further back than the Gen1, and the hammer wouldn't latch, so I had to turn the tapered sear catch on the front of the hammer down slightly to shorten the effective length and cocking distance about 0.030".... That did the trick.... I did some tethered testing, rebuilt a regulator for a 2200 psi setpoint, and then assembled the gun for the first time.... I used my 105 gr. steel hammer, because of the larger ports, and it worked great....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/357%20BRod%20Testing_zpsiaeglrjy.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/357%20BRod%20Testing_zpsiaeglrjy.jpg.html)

The "tiny tank" is what I use for testing and setting regulators, but it allows me to tether using the regulator I will be using on the gun.... and not have to waste a 500 cc bottle of air should I need to disassemble it.... Anyways, here are the results of both the tethered testing, and regulated at 2200 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/35%20BRod%20Big%20SS%20Valve_zpshqho4qvr.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/35%20BRod%20Big%20SS%20Valve_zpshqho4qvr.jpg.html)

I tested using the EunJins (I want to use them up and save the JSBs where possible)…. Initial tests at 1900 psi tethered showed the larger ports increased the velocity from 854 fps to 906 fps, an increase of 16 FPE.... slightly better than the difference in port diameter would have predicted, so I am very pleased with the new valve.... My Great White was just under 2900 psi, so I couldn't tether at that pressure.... I just connected directly to it, and tested the EunJins at 2800 psi, then the 119 gr. BBT HPs at about 2750, and lastly the 154 gr. Lee FN at 2700 psi.... Even though the pressures were less than the original testing I did with the ART-SS Valve with the smaller ports, I had higher FPE.... The 154 gr. bullet hit 202 FPE at just 2700 psi, so I am quite please with the way the new valve works.... With the 154 gr. I gained 15 fps at 200 psi lower pressure with the bigger ports....  8)

I then fitted the 2200 psi regulator with the "tiny tank", and tested with the EunJins and the 81 gr. JSBs (black line above).... With just a whisker of gap in the SSG I got 158 FPE, right what I was hoping for.... With the SSG backed out 3 turns (about 0.17" gap) the gun was shooting right at 150 FPE average with the two weights of pellets.... I shot a 10 shot string with the 81 gr. JSBs, and the ES was only 11 fps, with a low of 910 and a high of 921.... Seven of the 10 shots were 913-917 fps, so the valve is VERY stable.... The average was 150.7 FPE, and the 10 shot string dropped the pressure in my Great White by 41 psi (measured with a digital gauge)…. so the efficiency was 0.97 FPE/CI.... That should give me very close to 2 magazines (12 shots) at 150 FPE when I fit the 500 cc bottle and fill it to 3000 psi.... I can play with the SSG adjustment, and with hammer weight (I can go a bit lighter) to get the best balance between power and efficiency....

All in all, I am delighted with the way this project turned out.... The plenum is a bit small, and if it was increased to 1 cc per FPE the gun would likely hit about 160 FPE at the same setpoint pressure and air use, with greater efficiency.... I rather expected that to be the limitation on the performance.... and it looks like I was correct in my prediction, for both that, and the overall performance.... I hope next Spring I can find time to test it properly....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: bnowlin on November 26, 2018, 04:49:50 PM
Wow you made my head hut again. Really goo job.
Bobn the other Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: d_boom on November 29, 2018, 06:00:38 AM
Thanks for you sharing your experience, failures, with JB weld.  I will be careful
and avoid using it on airguns, I do not need to have leaks!  I have used JB weld
on several projects, but so far not on airguns.
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 29, 2018, 08:28:03 AM
JB Weld is an excellent product.... I just have had problems expecting it to seal against HPA....

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Gerard on November 29, 2018, 08:57:31 AM
Not sure how it relates to our potential uses of the product, but according to the JB Weld website:
Quote from: jbweld.com
J-B Weld has a tensile strength of 3960 PSI.
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Alan on November 29, 2018, 10:11:36 AM
Tensile strength is not the real issue—porosity is! I've looked several times, and I can't find out, nor will J-B tell you, what the porosity of their products are. Most epoxy consists of a polymer and a hardener, and they are not porous. But J-B weld, and several others, have metallic particles in the mixture. Your guess is as good as mine.
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Gerard on November 29, 2018, 10:22:00 AM
Ah, that makes sense. So total linear dimension of a given layer of steel-filled JB Weld might dictate relative air pressure resistance. Strange that in Bob's threaded insert application high pressure air found a path along the spiral of the thread... I always take care to mix JB Weld on a flat plastic sheet with a knife, pressing it out and stirring for a few minutes to ensure absolute blending with no air bubbles. Stirring in a cup can be a source of thousands of bubbles when blending any sort of epoxy and I don't want bubbles, so in anything where strength is critical I use the flat plate method for G-2 and other 'normal' epoxies. Learned that from my father in the 1970's. He did a lot of restoration work on marble counters and fireplaces in the San Francisco area, had to learn about the various stone powder pigments and how they affected strength and light reflective properties in epoxies. Bubbles were not acceptable in such high end repairs, so he always mixed on a large flat surface.
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 29, 2018, 03:06:53 PM
I always mix on a flat surface as well.... actually a notepad, and then just throw away the sheet of paper for a cleanup....  8)

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: rsterne on November 30, 2018, 06:32:24 PM
Today was consumed with all the little finishing touches on the three BRods…. I had a slow leak in the new .357 cal, which I found was a leaking plug on the bottom of the WAR tank block.... I had glued in that plug with JB Weld, and there was a slow leak spiralling up the threads.... Since I had glued the plug in, I had to heat it with a torch to break loose the epoxy, and once I got it out and cleaned it up, I shortened the plug 1/16" so that it would miss the ASA threads.... I had previously retapped the plug hole, and I went too deep, and the plug was interfering with the ASA threads.... I also removed the male Foster on the tank block and replaced it with a plug, since you fill the bottle through the regulator.... I sealed the plugs with Teflon tape, and that seems to have done the trick.... Once I had that done, I installed the 500 cc 3000 psi bottle, filled it to 3000 psi, and set it aside....

The .30 cal was leak free, so all I had to do was remove the male Foster on the tank block and replace it with a plug.... After a leak and velocity check, I also installed the bottle on that gun, and also filled it to 3000 psi.... Then it was the .25's turn, and I knew it had a serious leak....

It turned out there were actually three leaks, and it took me half a day to repair them.... The first two were easy, a loose plug and a loose gauge.... It was still leaking, so I stripped the gun down completely and replaced the valve O-ring.... but it wasn't that either.... Eventually I tracked it down to a leaking gauge, and once I replaced that it seems to hold air OK now.... I checked the velocity, and it was still what I wanted, so I installed the bottle on that one too, and filled to 3000 psi....

Here is what they look like, now that they are finished.... All three BRods use a modified .25 cal MRod receiver, bored out forward of the front 4-40 screws to accept a 5/8" OD barrel.... They all use a 500 cc, aluminum, 3000 psi bottle for the reservoir, and an SSG to control the hammer.... and have two gauges, one for the bottle pressure and one for the plenum pressure.... The main tubes are from WAR, I believe they were for the FLEX, and yield an 85 cc plenum, including the valve volume.... The tank blocks are also from WAR.... All of them use .25 cal MRod magazines and bolts, modded as necessary....

(http://i378.photobucket.com/albums/oo221/rsterne/BRod%20Project/Three%20BRods_zpszyubd9gu.jpg) (http://s378.photobucket.com/user/rsterne/media/BRod%20Project/Three%20BRods_zpszyubd9gu.jpg.html)

The top one is the .357 cal.... It uses a Synrod stock, and a Gen 2 trigger.... The barrel is a 1/2" OD, .357 cal, 26" twist TJs, 27" long, glued inside a high-modulas Carbon Fibre sleeve for added rigidity.... It has a steel hammer and a homemade SS valve, and the porting is 9/32" (0.281") or equivalent throughout…. The bolt nose is sleeved up to .357 cal, and the lockup lug is inceased to 10-32 for additional strength.... The mag is a 6-shot one-of that I modified myself....The regulator is mounted on the bottle, and set at 2200 psi.... This results in 2 mags (12 shots) at 146 FPE, using the 81 gr. JSBs at 900 fps....

The one in the middle is the .30 cal.... It uses a modified Bullpup stock that was a gift from Travis, and a Gen1 trigger.... The barrel is a 1/2" OD, .300 cal, 26" twist TJs, 25" long, also glued inside a high-modulas CF tube.... It has an MDS hammer and an ART-SS valve, one of the first production ones with the smaller poppet front end, and the porting is just over 1/4" (0.257") or equivalent throughout.... The bolt nose is sleeved up to .30 cal, and the lockup lug increased to 10-32 for additional strength.... The mag is a 7-shot from AirGunLab…. The regulator is also mounted on the bottle, and set at 2000 psi.... This results in 4 mags (28 shots) at 98 FPE, using the 50 gr. JSBs at 940 fps.... It will shoot the 44.8 gr. JSBs at about 980, and the 59 gr. NOE Hunter Magnums at 880 fps (101 FPE)….

The bottom BRod is the .25 cal.... It uses an airsoft AR stock, on an adapter that I made myself, and a PRod trigger and grips.... The barrel is a 5/8" OD, .250 cal, 17.7" twist LW, 23.8" long, with polygonal rifling.... It has an MDS hammer, and one buffer O-ring between that and the Cothran Powerhouse valve, with 0.257" or equivalent porting throughout, including an oblong barrel port.... The regulator is adjustable, and mounted in the COBRA tank block.... It was a sample from WAR, as I helped them design it, and is set at 1800 psi.... Having an externally adjustable regulator is nice with the Cothran valve, as you have to change the pressure to change the velocity.... This gun delivers 6 mags (48 shots) at 65 FPE, using the 34 gr. JSBs at 930 fps.... It is easy to increase that, or to reduce the pressure to about 1400 psi to use the 25 gr. JSB Kings if desired.... The way it sits, it will launch the Kings at about 1030 fps, which is way too hot....

This has been an interesting project, and I'm happy to say met all the goals I had.... I did some testing with bullets, running unregulated at 3000 psi, and while the performance was remarkable, I think they are much better guns regulated, and shooting pellets.... I hope to be able to do some testing next Spring, after the snow melts.... I must thank Travis for the big box of "spare parts" he sent me when he moved shop a couple of years ago.... Without that, these three BRods would have never materialized....  8)

Bob
Title: Re: Tale of THREE BRods - Adding a .357 Version
Post by: Alan on December 01, 2018, 04:04:20 AM
Wouldn't it be nice, if all you had to do now, was shoot them all every day? Alas, there are other things which must be done.
Title: Re: Tale of THREE BRods - .25, .30 and .357 Completed, Page 12!
Post by: rsterne on December 01, 2018, 08:14:41 AM
Two more years of Motel, and THEN I hope to have some shooting time....  ::)

So much to do, so little time....  ;D

Bob
Title: Re: Tale of THREE BRods - .25, .30 and .357 Completed, Page 12!
Post by: bnowlin on December 01, 2018, 09:06:11 AM
Great job Bob on the Brods.  With all those other things going on I haven't been able to shoot for a month.
Bobn