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Author Topic: Tale of Two BRods  (Read 8761 times)

rsterne

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Re: Tale of Two BRods
« Reply #15 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
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oldpro

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Re: Tale of Two BRods
« Reply #16 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.
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rsterne

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Re: Tale of Two BRods
« Reply #17 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
« Last Edit: January 11, 2017, 08:58:01 PM by rsterne »
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rsterne

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Re: Tale of Two BRods
« Reply #18 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....



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....



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....



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
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oldpro

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Re: Tale of Two BRods
« Reply #19 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
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rsterne

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Re: Tale of Two BRods
« Reply #20 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
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oldpro

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Re: Tale of Two BRods
« Reply #21 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.
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Motorhead

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Re: Tale of Two BRods
« Reply #22 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  ;)
« Last Edit: January 13, 2017, 12:46:49 PM by Motorhead »
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Scott

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Re: Tale of Two BRods
« Reply #23 on: January 13, 2017, 11:55:53 AM »
The Prod has more drag by far but Im telling you its TOUGH!!!
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rsterne

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Re: Tale of Two BRods
« Reply #24 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....



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....



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
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Motorhead

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Re: Tale of Two BRods
« Reply #25 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

« Last Edit: January 13, 2017, 03:01:19 PM by Motorhead »
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rsterne

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Re: Tale of Two BRods
« Reply #26 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
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rsterne

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Re: Tale of Two BRods
« Reply #27 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....



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
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Dairyboy

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Re: Tale of Two BRods
« Reply #28 on: January 13, 2017, 07:00:32 PM »
Can't wait to see what's next!
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Re: Tale of Two BRods
« Reply #29 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?
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