The AirGun Guild

General Category => PCP, C02, and Helium Powered Airguns => Topic started by: rsterne on November 20, 2016, 12:42:31 PM

Title: Regulated Disco Double
Post by: rsterne on November 20, 2016, 12:42:31 PM
Over a year ago, I suggested to Lloyd Sikes at the AirGun Lab, developer of the Disco Double, that he might consider making a regulator cartridge that could be installed inside the front upper plug that he supplies with his DD kits.... He thought it was a good idea, but life got in the way, so we didn't get around to doing the drawings until this Spring, and Lloyd made a prototype which exceeded our expectations.... He has since had some CNC'd, and has them in stock.... In addition, he has made an agreement with Eric Kuehn of Stalwart Arms to assemble and market the Disco Double kits.... I'll let Eric and Lloyd answer your questions about prices and availability (through PMs, please), the purpose of this thread is to build a Regulated Disco Double, and put the new regulator through it's paces.... Lloyd graciously supplied me with a regulated DD kit, and I purchased the rest of the parts shown in the photo below towards this project....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Regulated%20Disco_zps5bxfbyyj.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Regulated%20Disco_zps5bxfbyyj.jpg.html)

Starting at the top, the barrel is a .22 cal TJ's with a 1/2" OD, that Sean Pero and I designed a couple of years ago.... I have had it sitting on the shelf, awaiting a suitable project, and now is the time.... It is 0.217" land, 0.213" groove, with a 16" twist.... I have two projectiles in mind, both recent developments.... One is the new 34 gr. JSB Beast pellet, and the other is the recently released NOE .217 cal 30 gr. Bob's Boattail, which I designed to work in this barrel.... My mould is in the mail as I write this, and it has a Lyman HP pin in one cavity which will drop the weight a couple of grains.... Both of these will fit and function in a PRod magazine, and I will be building my own breech to hold that and the shrouded barrel.... The lightest pellet I plan on using is the 25 gr. JSB Monster, although I know that the 18 gr. Heavies are deadly in this barrel, as are the 16 gr. Exacts and Polymag Predators....

The next item down is a Discovery main tube from Crosman.... I will be drilling out the transfer port hole to accept a larger, 5/16" OD TP, and deburring it, plus drilling a tiny vent hole 9/16" from the front on the bottom, otherwise I plan no modifications to it.... The O-rings are part of the DD kit, which is below the main tube.... Not shown are the hammer and SSG, which have yet to be made.... I also plan on using a Carbon Fibre tube as a shroud, which will place the barrel in tension to stiffen it.... The tension will be adjustable using my Belleville washer setup at the muzzle.... and of course the associated parts have yet to be machined....

The regulated Disco Double tube kit arrived assembled, just as you see it in the photo above.... It consists of the same 120 cc reservoir used in the DD kit, good for at least 3000 psi safe working pressure.... At first glance, it appears almost identical to the original unregulated DD kit, I'll get to the differences in a minute.... To the right of the DD kit are a PRod gauge block, and a much modified Disco valve which I have already written about in an earlier thread.... In addition to bore-size porting throughout (0.219" exhaust port, 0.266" throat with MRod poppet).... the valve is fitted with high-tensile 10-32 screws allowing a MSWP of over 3000 psi....

Below the DD kit are a pair of barrel bands I got from Lloyd with the DD kit.... There are a variety available, these are for use with a BNM breech fitted with a 1" shroud.... I will be using a 7/8" CF shroud on my gun, so I will have to fit them with a larger cross-section O-ring to hold snugly on the smaller shroud.... To the right of those are a PRod trigger group and typical Crosman skeleton stock.... I will eventually modify the LoP and cheek rise on that to fit me....

Now to the important part, the new AirGun Lab Regulator.... It is a cartridge design, using thick 1/2" OD Bellevilles, with the piston retained in the rear of the upper plug (inside the upper tube) with a snap-ring as shown.... The air enters the upper reservoir through the hole in the center of the piston, which is threaded 6-32 for easy removal of the piston....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Regulator%20Rear_zpstgmwvekj.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Regulator%20Rear_zpstgmwvekj.jpg.html)

Looking at the front of the regulator, under the upper plastic cap, you will see an adjustment screw.... This allows moving the floating seat fore and aft, which allows you to externally adjust the setpoint pressure.... This is an exceptional feature, and part of our design criteria.... It was made possible by the position of the regulator at the front end of the upper tube, which now becomes the plenum.... a very large one at 135 cc.... The air pressure in the gun should be reduced below the current (or intended) setpoint (whichever is lower), so that the regulator piston is "open" and no pressure is on the seat before changing the adjustment, to avoid damaging the (replaceable) HP seal on the end of the piston.... IIRC, the adjustment range is about 500-2500 psi, Lloyd please correct me if I have that wrong....  :-[ .... The two protective caps, one for the adjustment screw and the other to cover the built in male Foster fill fitting, are identical, and interchangeable.... You can see them in place in the first photo....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Regulator%20Front_zpsggnjom5s.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Regulator%20Front_zpsggnjom5s.jpg.html)

The side view, below, shows that the new upper plug is a bit longer than the previous (unregulated) version, to allow room for the regulator piston.... Note that there are two O-ring grooves, but only one O-ring.... The reference vent for the center (spring) portion of the regulator is between those two O-ring grooves, on the lower side, hidden by the bottom tube.... When the regulator is in place, the O-ring is placed in the aft groove (as shown), and the venting occurs towards the front, through the hole I will drill in the main tube, just inboard of the threads.... If you want to run the gun without the regulator, you simply remove the regulator cartridge, and move the O-ring to the front groove.... The vent hole in the regulator is now behind the O-ring, which prevents venting.... This is an elegant and simple way to allow removal of the regulator without having to replace the upper tube.... because the vent hole in the tube is inboard of the threads, but outboard of where the O-ring seals.... Again, this shows the attention to detail that occurred with the synergy that Lloyd and I have when working on projects like this.... I take great pleasure in working with him because of that....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Regulator%20Side_zpsjasmwv3k.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Regulator%20Side_zpsjasmwv3k.jpg.html)

Anyway, there is the starting point for this exciting new project, and the details on the new AirGun Lab regulator for the Disco Double kits.... In addition to it being an option on the new DD kits (they all now share the new upper plug that accepts the regulator cartridge).... they are also available as a retrofit for the previous DD kits which were unregulated.... All you need is the new upper plug with regulator, shorten the hollow connecting bolt a bit (to miss the adjusting screw) and drill the vent hole in your main tube, and you're good to go.... You could even reinstall the original DD upper plug, or go back to a Crosman fill fitting, and the vent hole in the tube isn't an issue because of it's location.... This means complete interchangeability of parts, with no obsolescence, again one of our design criteria.... I'm looking forward to getting started on my new Regulated Disco Double....

Bob


Title: Re: Regulated Disco Double
Post by: Rdsail on November 20, 2016, 03:10:07 PM
very cool! I talked to Lloyd a while back and he mentioned that he was working on this Disco regulator that can be externally adjusted. Makes me thick about building one.



Title: Re: Regulated Disco Double
Post by: Motorhead on November 20, 2016, 05:50:47 PM
If I see this right ?  ... upper tube is HP and lower containing REG on the end is a LP tube ?
Title: Re: Regulated Disco Double
Post by: rsterne on November 20, 2016, 06:45:14 PM
Nope, other way around.... The lower tube (with the Foster) is the HP reservoir, and the upper tube (the original Disco main tube) has the regulator in the front of it and serves as the plenum.... The valve is in the upper tube, as per usual....

Bob
Title: Re: Regulated Disco Double
Post by: Motorhead on November 20, 2016, 08:54:52 PM
Nope, other way around.... The lower tube (with the Foster) is the HP reservoir, and the upper tube (the original Disco main tube) has the regulator in the front of it and serves as the plenum.... The valve is in the upper tube, as per usual....

Bob

LOL ... down side up orientation, forgot about that  :o

That said ... so you have the main tube w/ valve being essentially one big plenum running at regulated pressure ?
Good way to get a very stable shot to shot velocity so long as HP storage feeding it is above Regs set pressure.
Title: Re: Regulated Disco Double
Post by: rsterne on November 21, 2016, 09:06:24 AM
That is correct.... The plenum is huge, big enough to handle pretty much anything that would be realistic with a Disco.... I did a calculation in another thread that showed that using this setup for a .35 cal pellet shooter, with a Cothran valve, and the regulator set to 2000 psi.... should give 5 equal shots at 135 FPE with 78 gr. JSBs.... I know of no other setup for a Disco (other than a bottle) that could do that....

Just to give an idea, a stock Disco reservoir is 135 cc, and the Disco Double lower tube is about 120.... If you set the regulator to 1500 psi, and fill the lower tube to 3000 psi, the equivalent total volume at 1500 psi is 375 cc.... Without the lower tube, if you installed a regulator in the upper tube that resulted in a 100 cc HP reservoir and a 15 cc plenum, and then filled the upper tube to 3000 psi, you would have the equivalent of 215 cc.... If you only used the stock 2000 psi, that would be only 148 cc available at 1500 psi....

Bob
Title: Re: Regulated Disco Double
Post by: grumpy on November 21, 2016, 11:19:05 AM
I am glad to see Lloyd suggested this.
Title: Re: Regulated Disco Double
Post by: rsterne on November 21, 2016, 02:32:34 PM
Don't quite understand, Dave, but whatever....  ???

Today I drilled out the transfer port hole in the Disco tube to 5/16", and while I had it mounted in the mill I lengthened the front of the cocking slot for the hammer by 0.20".... I will be increasing the hammer stroke, and just wanted to make sure the cocking pin won't hit the end of the slot on firing.... I then deburred all the slots and holes, paying particular attention to the gauge hole, which makes a great cheese grater the way Crosman machine it, but not very kindly to the O-rings you have to slide past it.... I pay particular attention to the front and especially the back inside edge, rounding it so that the O-rings can slide past it without getting torn.... Not doing that the first time you have a Disco apart is a big mistake.... I then carefully cleaned the inside of the main tube....

I mentioned before that the bands I got from Lloyd that hold the tubes together were for a BNM breech with 1" shroud.... The upper portion has an O-ring groove machined into it for a #022 O-ring, that will hold that diameter shroud.... I will be using only a 7/8" OD shroud, but I found that by using #212 O-rings I could used the same bands, as they have the same OD but the smaller ID I require.... However, the groove in the bands was too narrow, so I chucked them I my lathe and put a taper on the side of each groove so that they were 0.140" wide at the inside, in sort of a half-hexagon shape.... I did NOT have to cut the groove any deeper, just wider at the inner edge.... With a 70D O-ring installed, they fit the 7/8" tubing I have nicely, a snug, sliding fit with the O-ring compressed about 0.010".... This will hold the shroud well, without being rigid.... and there is no way the O-ring can pop out once the tube in installed....

I checked the fit of the valve, ground a notch in the top rear to miss the forward breech screw location, and also ground a notch in the bottom rear to allow better venting of the space between the hammer and valve through the hole behind the bottom screw.... I then  disassembled and carefully cleaned the valve, lubed the stem and O-ring and put it back together.... I then lubed the valve and gauge block O-rings, slid the valve into place, installed the 10-32 screws, then installed the gauge port and a 3000 psi gauge.... As the O-rings pass the gauge hole, be VERY careful they don't get cut.... I use my fingernail, or a small flat-bladed screwdriver, to coax them past my nicely rounded edge, but you still need to be careful and work slowly.... I rolled a #016 O-ring onto the upper plug of the Disco Double kit, where it butts against the end of the main tube, lubed the O-ring that seals inside the tube, and screwed the tube onto the upper DD plug that contains the regulator.... Just before it contacts the O-ring, have a look at where the gauge is in relation to the lower DD tube, and stop threading it on when the gauge lines up with the lower tube and the O-ring is under the least compression possible.... Its only purpose is to fill the gap between the end of the upper tube and the upper plug for appearance and to keep the dirt out.... There is plenty of thread engagement without cranking it that last turn and squeezing the O-ring out of the groove....

I then temporarily installed the trigger group so that I could align the position of the lower tube with it.... I slid the narrow tube band (the one without the Picatinny rail) onto the two tubes, right back to the end of the lower tube, leaving only the flange on the aluminum plug past the band.... Once I was happy with the alignment of the tubes I snugged the setscrews on the bottom of it, turned the assembly around and viewing from the front made sure the tubes weren't twisted and sat parallel with each other.... I then tightened the setscrews in the tube band, being careful not to tighten them so much they would crush the tube, which is thin there because that is where it is threaded.... This completed the pressure assembly, and it now looks like this....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Disco%20Double%20Assembly_zpsvm0nu4jj.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Disco%20Double%20Assembly_zpsvm0nu4jj.jpg.html)

At this point, it was ready for a leak test.... I slowly put in 1000 psi, and checked for leaks with soapy water on a small brush.... Finding none, I the gradually filled the reservoir, 200 psi at a time, allowing for the pressure to equalize and kept my eye on the gauge, which reads the pressure downstream of the regulator, so it will tell you the setpoint.... It stopped and held at 1600 psi, so I stopped filling at 2000 psi, waited a few minutes to be sure it hadn't crept up (it hadn't budged), and since I was still attached to my Great White I bled the line very slowly, which will often leave the check valve in the Foster open and allow you to bleed air from the bottom tube.... It worked, and once I got the tube down to 1400 psi I checked the gauge on the gun, and it still read 1600 (as it should).... I then quickly bled the air from the line to my tank, leaving 1400 psi in the lower tube and 1600 in the upper.... I wanted to increase the setpoint of the regulator, both because I expected to need a bit more pressure for this project, and because I wanted to play with the adjustment.... That meant that I had to bring the pressure in the upper tube down to less than the current setpoint, so I didn't damage the HP seat in the regulator....

The only way to do this, or at least the easiest way, was to fire the gun, so I temporarily installed the trigger group, a hammer, spring, and RVA, and making sure the transfer port was facing away from me, pulled the trigger.... I wish I had rembered to remove my hearing aids and put in my ear plugs, because it was LOUD!.... Fortunately, my hearing aids have a "clamping circuit" that prevents loud noises from getting through, so the actually act like (rather noisy) ear plugs.... Just the one shot dropped the pressure to 1400 psi, so now both tubes were below the current setpoint.... Since I was going to increase the setpoint, I didn't need to remove any more air.... If I had been going to lower it, then the pressure in both tubes would have to be lowered BELOW the new setpoint to make sure you don't damage the HP seat.... To increase the pressure you have to move the seat OUT, towards the front of the gun.... This allows the piston to move further before closing the HP seat, which compresses the Belleville springs further.... That takes more force, which means more pressure, and you end up with a higher setpoint.... To lower the pressure you need to do the opposite, you need to move the seat IN.... If you didn't bleed air from the gun, then you would be screwing the adjustable metal seat into the plastic seat on the end of the piston, and could easily damage it.... To repeat....

Adjuster OUT (CCW) increases the setpoint pressure....  Adjuster IN (CW) decreases the setpoint pressure....

If the screw is hard to turn, you probably forgot to bleed the pressure down, STOP and make sure both tubes are BELOW the lowest pressure setpoint you need.... The slot in my adjuster, viewed from the front, was at about a 45* angle, from 10:30 to 4:30 o-clock.... I decided to try 1/8 turn CCW, so I set the slot horizontal, at 9:00 to 3:00 o'clock.... The screw moved with noticeable drag from the O-rings that seal it, but was not difficult to adjust.... I then reconnected the Foster to my Great White and added 200 psi at a time, watching the pressure gauge to see how much I moved the setpoint.... It was almost exactly 200 psi, it now settled in and stayed at 1800, which is pretty close to where I think I need it.... certainly close enough for initial trials.... I continued filling the lower tube to 3000 psi.... let it sit for a while to cool, and topped it up before coming in to take the photo and write this post.... The assembly will sit under pressure while I continue to work on other parts of the gun as a leak test.... Note that if the gauge eventually shows a pressure drop, if would indicate that the leak is downstream of the regulator.... If there was a leak upstream of the regulator, the gauge (in theory) would not give you an indication of that.... However, the next time you went to fill from a tank, you could hear the check valve in the Foster click below the pressure you left the gun at....

Bob
Title: Re: Regulated Disco Double
Post by: grumpy on November 21, 2016, 03:39:44 PM
Sorry Bob, sorta got cut off in my post. What I meant is Lloyd was telling me how well my efficient my .257 Brod is shooting with the Cotrane valve an his regulator. Thought he mentioned to me when we last spoke that he was going to suggest regulating your Disco to help its efficiency.
Title: Re: Regulated Disco Double
Post by: rsterne on November 21, 2016, 06:40:12 PM
Ahhhhhhh, now I understand.... Lloyd and I have been working together on this regulator for "well over a year" according to him....  ::) .... I was actually the one who first suggested it.... We are both working on Cothran valves, his in an MRod (yours?) and mine in a Disco Double, but not this one, this will have one of my valves, as it's only .22 cal and I can get full bore-area ports no problem, have done it many times....

No idea if the way the guns are being configured is the way they are going to stay, of course.... I may end up swapping parts around at some point.... That's the nice thing about Crosman LEGO airguns, lots of interchangeablity....  8)

Bob
Title: Re: Regulated Disco Double
Post by: grumpy on November 21, 2016, 07:13:03 PM
I'm sorry, did not mean to imply anyone took an idea from another. Thought maybe Lloyd shared the sucess of the reg in mine to help you. Now the Coltrane valve is a semi new add on to mine. He liked it with the regulator better then his own valve design.

Dave
Title: Re: Regulated Disco Double
Post by: rsterne on November 21, 2016, 08:03:39 PM
It's all good, Lloyd and I share back and forth all the time....  8)

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on November 22, 2016, 06:16:32 PM
Since I am using a PRod pistol grip trigger group and skeleton buttstock, I needed a forearm of some kind.... I ordered a pair of tube bands from Lloyd with the thoughts that I could probably come up with a way to mount a slotted piece of black 1-1/4" ABS Pipe between them to serve that purpose.... Here is the adapter I made, shown next to a tube band....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Mount_zpsuyej1fj8.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Mount_zpsuyej1fj8.jpg.html)

It is made from a piece of 1-3/8" bar stock, drilled out to 1" and then bored out to 1.096" to the same depth as the tube band.... I then machined away two 90* segments, leaving the other two to fit around the lowest portion of the band.... This will mount the tubing concentric with the lower tube, as it is 1-3/8" ID so will just slide over the adapter.... I had to machine away the top portion to miss the upper tube (the Disco main tube), and the ABS pipe will have to be slotted to miss that tube as well.... Here are the two adapters, slid onto the tube bands, and sitting in the appropriate locations on the double tube assembly.... The front one can be positioned anywhere I want, depending on the length forestock I choose....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Stock%20Mounts_zpslbhsfhpz.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Stock%20Mounts_zpslbhsfhpz.jpg.html)

As you can see, the adapters are on the inside of the tube bands, and the split piece of pipe will simply slide over them.... I can extend the pipe towards the rear, closer to the gauge if desired, as the setscrew portion of the rear band is below the diameter of the adapter.... I had to just file the corners slightly to prevent them dragging on the ID of the pipe.... On the front, you can see the Picatinny mount which is part of the front tube band.... I projects high enough above the adapter to clear any standard Weaver mount or ring, but I may have to notch the front of the tube a bit to clear the BiPod mount I have, it's a bit wider than the tube band on both sides....

This is going to work perfectly.... I will drill both sides of each adapter and tap the tube band for small screws, and also drill the sides of the plastic pipe and tap the adapters so that everything is rigid when assembled.... That, and cutting a wide slot in the pipe, are all that remain to complete the forestock....

Bob

Title: Re: Regulated Disco Double
Post by: Christopher on November 23, 2016, 02:20:46 AM
Looking good Bob.

Chris
Title: Re: Regulated Disco Double
Post by: rsterne on November 23, 2016, 06:24:06 PM
I completed the Forestock today.... The stock itself is a foot of 1-1/4" ABS pipe with a slot cut in the top to clear the main tube.... It is mounted with four 6-32 pan head screws tapped into the adaptors I made yesterday, which are secured to the tube bands I got with a pair of 6-32 setscrews each.... Here is what the assembly looks like.... I slid a shroud I borrowed from my other Disco Double into place just to see what it looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Forestock_zpssxoqjegk.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Forestock_zpssxoqjegk.jpg.html)

As you can see, the Picatinny mount protrudes below the stock at the front, and it can be used for any accessory, such as a flashlight, laser, or a BiPod.... I fitted the PRod trigger group and the Skeleton stock, along with a BiPod for the photo below.... There is no breech on the gun, but it gives you an idea of what it will look like when finished....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Assembly%20on%20BiPod_zps4wuxnonm.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Assembly%20on%20BiPod_zps4wuxnonm.jpg.html)

I used a holesaw to cut a circular hole in the bottom rear of the stock and then tapered the sides for appearance.... In profile view the stock hides the gauge, but it is easily readable from the bottom, as in the photo below....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Forestock%20and%20Gauge_zpsw8rhrhfh.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Forestock%20and%20Gauge_zpsw8rhrhfh.jpg.html)

The forestock is in a great location, and is long enough for shooting offhand or prone, and the BiPod is in an ideal location, it can be folded forward, and remains within the overall length, even if the legs are extended.... I'm very pleased with the overall proportions and appearance, and although it doesn't yet have a breech or barrel, it's shaping up to be extremely light and well balanced....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on November 24, 2016, 01:34:28 PM
Today I made the hammer for the new gun, and using a bunch of parts I had laying around and/or borrowed from my other Disco Double, I assembled an SSG.... They aren't anything special....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Hammer%20and%20SSG_zpswbxmvafa.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Hammer%20and%20SSG_zpswbxmvafa.jpg.html)

The hammer is a simple cylinder, 1.30" long (like a stock Disco hammer) and the front end is as per usual, flat in the middle with a taper on the edge for the sear to catch.... It is, however, drilled to 3/8" to allow larger hammer springs, the hole is 3/8" deeper than stock (7/8" total), and the cocking pin is moved back as far as I could.... There is a notch on the top at the front to clear the rear breech screw location, should I decide to use that.... With the notch in the valve I have the option of either location, or I can (and probably will) drill and tap the tube in between for a larger SHCS for the new breech.... The hammer weighs virtually the same as a stock Disco hammer, at 57 grams....

The SSG is the original type, where the guide runs through the gap adjuster (the large hex bolt) with an O-ring between that and the preload adjusting nut.... The spring is from a QB78, and is currently set up for about 0.4" preload (just under 7 lbs.).... As shown in the photo, the gap is zero, the end of the spring guide just touches the end of the hole in the hammer when it is sitting on the valve stem.... I have 0.72" of hammer travel total, so with a 0.020" gap (1/2 turn) I will have 0.7" of travel "under power", and the maximum force when cocked with be 19 lb.f.... I know from past experience that should be more than I need for this gun, so fully expect to be able to use a lighter spring or at least less preload when the gun is completed.... but for now this should work, and be able to reach maximum velocity (ie the plateau) in .22 cal with the 34 gr. JSBs, which is the heaviest I will be using....

Everything in or below the main tube is now done, so I guess it's just about time to start thinking about making the breech and machining the barrel to fit....

Bob

Title: Re: Regulated Disco Double
Post by: rsterne on November 28, 2016, 04:38:46 PM
I had a chance to get started on the breech (receiver) today.... I finished the design and drawings over the weekend, so it was time to make chips.... I started with a piece of 1" x 1-1/2" 6061-T6 Aluminum 7.5" long.... The breech is only 7/8" x 1-1/4", so the first order of business was to reduce the dimensions to that by milling.... My lathe attachment only has 6.5" of travel, and the largest end mill I have is 1", so I had to make multiple passes and reposition the work, so it took most of the morning just to do that.... After lunch I centerdrilled both ends where I wanted the barrel (equidistant from the top and sides for appearance), and then mounted it between centers on my lathe, and gripped it in a 4-jaw chuck.... I turned the stub to fit inside the shroud, and then drilled a 3/8" hole just over half way through.... I then swapped the chuck to the 3-jaw, reversed the breech, held it by the shroud stub (which is centered with the hole for the barrel) and drilled from the other end until the two 3/8" holes met.... They were pretty close, as I could run the (long) drill right through the entire length.... I then swapped over to a 1/2" long drill and drilled the hole straight through that size in one operation from the back end, with the shroud stub still held centered in the chuck.... That cleaned up any slight misalignment in the 3/8" holes, and gave me a 1/2" bore straight through from end to end....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Breech%20Roughed%20Out_zpsvvifsirv.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Breech%20Roughed%20Out_zpsvvifsirv.jpg.html)

I used an adjustable reamer to carefully bring the bore up to the size of the Cold Rolled Steel rod I will use for the bolt, which is a couple thou smaller than the barrel OD, so the barrel will have to be polished to fit.... However, the bore is straight enough I can slide the piece of CRS for the bolt straight through.... It's the best alignment I have ever had between the bolt and barrel, that usually causes me problems.... so I'm off to a good start....

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on November 28, 2016, 06:21:53 PM
Looks like another winner for you, Bob.

Joe
Title: Re: Regulated Disco Double
Post by: oldpro on November 30, 2016, 08:40:24 AM
 Good start keep up the good work. Keep us posted.
Title: Re: Regulated Disco Double
Post by: rsterne on November 30, 2016, 08:54:13 PM
Yesterday I got the concave in the bottom of the breech machined with a 7/8" ball end mill.... Today I spent the day in the shop and got all the holes drilled and tapped and the notches milled out for the magazine and the front barrel band, and the slot for the cocking pin.... plus the dovetail for the scope.... Here are photos of the breech as it looks at the moment....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Breech%20Top_zpsbdrohilf.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Breech%20Top_zpsbdrohilf.jpg.html)

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Breech%20Bottom_zpsajkc61bw.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Breech%20Bottom_zpsajkc61bw.jpg.html)

I tried mounting it, and it bolts onto the tube properly, and the stub for the shroud lines up great with the barrel bands, the shroud slides right into place.... I still have to machine the slot for the bolt handle, and the recess in the bottom for the cocking pin to swing to the opposite side to the handle.... I also have to make the band that fits into the notch in the front and holds the front of the breech down tight to the main tube....

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on November 30, 2016, 09:01:47 PM
I like the way the breech secures to the band.

Joe
Title: Re: Regulated Disco Double
Post by: Hobbyman2007 on December 01, 2016, 06:47:23 AM
I sure wish the manufacturers (crosman/Benjamin) would follow your lead on the design of your breech Bob. Nothing worse than that absolutely useless 4x40 breech screw crosman uses. Nice work
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 01, 2016, 07:14:24 AM
I sure wish the manufacturers (crosman/Benjamin) would follow your lead on the design of your breech Bob. Nothing worse than that absolutely useless 4x40 breech screw crosman uses. Nice work

Ditto.
Title: Re: Regulated Disco Double
Post by: rsterne on December 01, 2016, 08:04:04 AM
I still use a small screw there, I drill and tap for a 4-40 between the two Crosman locations.... I use a standard SHCS, I can get away with that because my breech is thicker in that area.... It ties down the center of the breech near the transfer port just to prevent flex where the huge cutout is for the magazine.... Most of my standard Crosman breeches end up with a slot ground in the 4-48 screw head....  ::)

The front band I use has two long 4-40 screws tapped into the band, which is flat on the top.... It fits between the front of the trigger group and the gauge, there is just enough room there for a 1/4" wide band....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 02, 2016, 07:47:35 PM
I spent most of the afternoon and evening modifying a pair of .25 cal MRod mags to use the .22 cal wheels, so now I have .22 cal mags that are interchangeable with my .25 and .30 cal mags.... This will allow me to use any of the three calibers in the Regulated Disco Double.... It was far from a simple "drop in the .22 cal wheel", which is what I had been told.... If you want to read the saga of this conversion, you can do so here.... http://www.gatewaytoairguns.org/GTA/index.php?topic=117960.

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 02, 2016, 08:13:46 PM
Seems you've out done yourself, Bob.  Any pics for us to look at?

Joe
Title: Re: Regulated Disco Double
Post by: rsterne on December 02, 2016, 10:03:44 PM
Here are pics of the finished mags, Joe....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Finished%20Mags_zps9x9nd2ae.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Finished%20Mags_zps9x9nd2ae.jpg.html)

You can see the #011 O-ring through the clear cover, it partly obscures the numbers on the wheel.... In the back view, if you look carefully you can see a ring of clear plastic around the head of the pellet, where the hardened glue made the through hole smaller.... Note how perfectly the pellet is centered in the bore now....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 03, 2016, 05:45:45 PM
Today I did some more work on the breech.... I machined the J-slot for the bolt handle and drilled and tapped the back for the velocity adjuster....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Bolt%20Slot_zps180fvgqq.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Bolt%20Slot_zps180fvgqq.jpg.html)

The bolt is a probeless, retracting style, with a flat nose that chambers the round when pushed forward, then you rotate the handle downwards and withdraw it into the lower slot.... In the lower slot you can see a 1/8" steel pin, the position of which is adjustable by the 8-32 SHCS on the back of the breech.... Up from the bottom, near the back, I drilled and tapped a 6-32 hole for a setscrew pressing a small piece of Delrin against the bottom of the 8-32 screw as a brake, to keep it from self-adjusting.... There is a total of 9/32" of adjustment, which works out to 9 turns on the adjusting screw.... When fully retracted, the front of the bolt face is flush with the back of the barrel port, and fully forward it chokes it off almost completely.... This allows a very wide range of velocity adjustment, currently it is set about in the middle for the photo, so you could see the pin that limits the distance the bolt can be retracted....

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 04, 2016, 04:20:16 PM
Thanks for those awesome pics, Bob.  Keep us in the loop.

Joe
Title: Re: Regulated Disco Double
Post by: rsterne on December 05, 2016, 02:53:12 PM
Today I worked on the barrel tensioning system.... I have been using barrel tensioners for a few years now.... They are nothing new, of course, even Crosman used a tensioning system in (IIRC) its Mk.1 CO2 pistol, to stiffen and protect the thin "soda straw" barrel.... What I did differently was to utilize Belleville Washers at the muzzle to provide a variable tensioning system, that would look after a large portion of the thermal expansion as well.... Barrel tensioners are beginning to be more widely used to stiffen our rather long and slender barrels in "upscale" limited production PCPs, two notable ones are the FLEX and the Slayer (and possibly the Thomas as well? ).... The basic idea is to use a shroud, with a much larger OD than the barrel, and by tensioning the barrel at the muzzle and putting the identical compression load in the shroud, the assembly acts like it had the much larger OD of the shroud, instead of the smaller OD of the barrel.... As you increase tension, just like on a guitar string, the vibration frequency of the barrel increases, and the amplitude of the vibration decreases.... If the shroud is mounted solidly to the receiver (or part of the receiver as in my Monocoque design), then even the primary vibration of the barrel (the barrel waving up and down or side to side like a flagpole) can largely be eliminated or at least minimized.... The goal, of course, is to make the barrel stiffer and increase accuracy.... The guns I mentioned above all do this extremely well.... The tension can be considerable, Tom at American Air Arms estimated the tension on the Slayer barrel at about 800 lbs. achieved by torgueing the barrel nut....

If the barrel and the shroud are made of the same material, then as the temperature changes, they will change length by the same amount, and the tension will stay a constant.... The same thing will happen if the Thermal Expansion Coefficients are identical, or at least very similar.... However, if the barrel and shroud expand at different rates, the tension will either increase or decrease, depending on which expands more.... If the tension is applied by torqueing a nut, just a few thou can make a huge difference in the tension.... That is where I got the idea of using a short stack of Belleville washers (disc springs) at the muzzle.... They act like a very stiff spring, and so a few thou change of length (and therefore preload on the washers) won't change the tension near as much as with a rigid connection.... The stack of five 1" OD x 1/2" ID x 0.073" Bellevilles I am using in this case have a spring rate of 15,000 lb/in, which over their total travel of 0.090" means they can develop up to 1335 lbs. of force.... If the preload is 0.060", the tension will be 900 lbs. and a 0.010" change due to expansion will only change the tension by about 150 lbs.... Without the Bellevilles, a 0.010" differential change in length could drop the tension to virtually zero.... So to summarize, the intention of the Bellevilles is to allow for differential thermal expansion between the barrel and the shroud.... and to make adjustment easier and more consistent....

One of the things a shroud can be used for is to use the internal volume to reduce the residual air pressure at the muzzle by having the shroud longer than the barrel.... In some PCPs that length is filled with baffles to further attenuate the report.... However, just the shroud can do quite a bit, providing some of the muzzle blast is contained within it.... In the Slayer, the nut used to tension the barrel is perforated to allow some of the HPA to bleed back into the shroud.... Up until recently, I could not figure out a way to do that with the Bellevilles in the way.... While working on another project with John Kopaz and Lloyd Sikes I suggested the idea of using a vented barrel extension to position the Bellevilles ahead of the muzzle, and vent some of the residual muzzle pressure back into the shroud.... I have dubbed this arrangement the "Vented Barrel Tensioner", or VBT.... At its heart is a tube threaded onto the muzzle, with four 1-caliber holes at 90* to each other to allow some of the muzzle blast to enter the shroud.... The front of that tube is pulled on by the Belleville washers.... There is a collar which the tube slides through to center it and transmit the compression load from the Bellevilles into the shroud.... The front of the tube is threaded, and a nut, made to enclose the Bellevilles, allows them to be compressed to tension the barrel.... Here is what it looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/VBT%20in%20Shroud_zpsntf5owbh.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/VBT%20in%20Shroud_zpsntf5owbh.jpg.html)

The photo above shows the VBT assembly on the front of the shroud.... There are a pair of flats on the front to adjust the tension with a 5/8" wrench.... The assembly adds less than 3.0" of length past the original muzzle, one of the great advantages of using this system....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Vented%20Tensioner%20Assembly_zpsc3ntz7kx.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Vented%20Tensioner%20Assembly_zpsc3ntz7kx.jpg.html)

With the shroud removed, you can see what the assembly looks like.... The Bellevilles are hidden within a chamber formed by the adjustment nut and the compression collar that butts against the front of the shroud.... In this photo, the Bellevilles are under no compression, while in the top photo, they are fully compressed.... Note the difference in how much of the flange on the collar you can see behind the chamber portion of the nut, which gives a visual indication of the amount of tension applied.... The total travel is only 0.090"....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Vented%20Barrel%20Tensioner_zpspswrvq1w.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Vented%20Barrel%20Tensioner_zpspswrvq1w.jpg.html)

In the third photo, the adjustment nut has been removed, and you can see the chamber inside for the Bellevilles.... It threads onto the front of the perforated tube, which threads onto the front of the barrel.... I used 1/2"-20 NF threads on both ends, and in fact the threads on the front of the barrel are exactly what is required to mount a Hatsan Air Stripper, leaving my options open.... There is a slight recess in the back of the perforated tube for the O-ring on the barrel, the purpose of which is to allow the tube to be tightened onto the muzzle but allow a slight amount of movement at that joint.... This allows the tension to keep the tube perfectly aligned with the bore.... The tube is drilled through using the 29/64" tap drill to a depth of 1.8", and there are about 1" of threads inside.... This creates a chamber in front of the muzzle where the four holes are drilled to vent the muzzle blast out into the shroud.... The remainder of the tube is currently drilled to 1/4" (this gun is a .22 cal), although I may drill it out slightly larger, and it would have to have a larger hole for larger calibers.... There is enough material to handle at least a .30 cal barrel with plenty of clearance for the bullet....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Barrrel%20Tensioner%20Parts_zpsvunfq67a.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Barrrel%20Tensioner%20Parts_zpsvunfq67a.jpg.html)

The last photo shows the Bellevilles washers and the collar they rest against that fits snugly inside the shroud and transmits the compression load to it.... The perforated tube was made from a piece of 5/8" CRS, with the front portion machined down to 1/2" to fit through the Bellevilles and threaded for the adjustment nut, shown to the left of it.... The shroud tube I am using is 7/8" OD Carbon Fibre, with a 3/4" ID, which only leaves a 1/16" gap around the holes.... While this is way more than the bore area, using a larger 1" OD shroud would allow more room for the muzzle blast to turn the 180* to flow back into the shroud, and would also greatly increase the available volume inside the shroud for expansion.... It would also eliminate the step down in OD from the 1" Bellevilles, bringing the shroud OD to the same size as the collar OD and the Bellevilles, making the VBT appear less bulky (relative to the larger shroud).... The VBT could also be scaled up for larger barrel diameters (to handle larger calibers), by using larger Belleville washers, of course....

Bob
Title: Re: Regulated Disco Double
Post by: alamih on December 06, 2016, 07:22:50 AM
Hi Bob
excellent job as usual, I'm curious what happend with Monocoque rifle project  from another
airgun forum
Best regards
Greg
Title: Re: Regulated Disco Double
Post by: rsterne on December 06, 2016, 08:46:32 AM
I've been waiting for a chamber reamer and bullet moulds for a year now.... have the moulds now, going to have to make a reamer myself, I guess....

Bob
Title: Re: Regulated Disco Double
Post by: alamih on December 06, 2016, 09:17:45 AM
thanks for answering
I'm looking forward to the progress of your work
Greg
Title: Re: Regulated Disco Double
Post by: rsterne on December 07, 2016, 04:29:53 PM
I threaded the muzzle of my .22 cal barrel today, and it turns out it is 28", not 25" as I thought.... I will use is as is for now, until I find out what the velocity is with the 34 gr. Beasts, and maybe shorten it later (who am I kidding!).... Anyway, I assembled it for the first time to day, so that I could see it, take a photo, and weigh it....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/First%20Assembly_zpsgmrg2gcs.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/First%20Assembly_zpsgmrg2gcs.jpg.html)

The overall length is 46.5" and it weighs 6 lbs. 10 oz.... I still have to make the bolt and the front breech band, and alter the stock, but it is easily going to make my 7 lb. goal without the scope.... so I'm a happy camper.... I think it looks pretty slick as well, and it balances right in the middle of the forestock....  8)

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 07, 2016, 08:20:12 PM
So, how soon can we expect to see any numbers and hunting pics, Bob?

Joe
Title: Re: Regulated Disco Double
Post by: rsterne on December 07, 2016, 08:33:49 PM
At least another week before the first test firing.... I still have to make the breech band, machine the chamber, leade, O-ring groove and port in the barrel, make the bolt and machine the recess in the breech for the cocking pin.... I am still hoping to get a chamber reamer from Sean Pero, but he isn't answering me.... If I get to the point the chamber is the only thing left, I'll make one myself.... I still need to cast some of the new 30 gr. BBTs as well.... No hunting until next spring, however....

Bob
Title: Re: Regulated Disco Double
Post by: grumpy on December 08, 2016, 06:00:26 AM
Bob, your handiwork never ceases to amaze me !
Title: Re: Regulated Disco Double
Post by: rsterne on December 09, 2016, 02:13:43 PM
After shovelling snow this morning, I got back into the shop and made the front breech retaining band and the bolt and handle....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Bolt%20and%20Band_zpspnnqlj9k.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Bolt%20and%20Band_zpspnnqlj9k.jpg.html)

I notched out the ID of the band with a small mill so that it can be slid over the tube from the rear with the valve screws in place, something I always seem to forget and have to do by hand afterwards with a file....  ::) .... The bolt nose is only roughed out oversize, it will be finished in diameter and to length after the barrel is chambered and the O-ring groove cut.... It also needs the hole for the cocking lug drilled and tapped into the bottom, but at least the main body and handle are done....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 14, 2016, 08:42:33 AM
Minus 27*C here this morning.... put the heat on in my shop, hopefully it will be warm enough by lunchtime to do some bullet casting.... The plan is to break in my new NOE 30 gr. mould....

Bob
Title: Re: Regulated Disco Double
Post by: Christopher on December 14, 2016, 02:37:45 PM
Can't hardly wait for some test results ;D

Chris
Title: Re: Regulated Disco Double
Post by: rsterne on December 16, 2016, 06:19:11 PM
I guess I can't put it off any longer, I have to make my own chamber reamer.... I have made a few before, but they have been a basic, single flute design.... I thought that a six-flute style was overly complex for my machining skills, so I decided to try one that uses three flutes.... The starting point is a piece of O1 (Oil Hardening) Drill Rod, I chose a piece of 3/8" diameter.... I chucked it up in my lathe, and carefully turned it down to 0.001" over the groove diameter of my TJ's barrel for the chamber portion.... Using the compound rest set at 1* off parallel with the bed, I then machined a taper from that diameter down about 0.010" smaller at a point 0.2" from the end to create the leade.... The remaining part at the end I machined down for the pilot, so that it would smoothly slide into my barrel blank, and that took about 0.0015" smaller than the measured land diameter.... I tried 0.001" but it was a whisker snug, and you can't afford to have the pilot hang up during the reaming process and damage the rifling.... I then turned the shank down about 0.020" smaller than the chamber so that it wouldn't hang up at full depth.... At this point, the reamer blank looked like this.... The front, pilot section of the reamer is on the right....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Reamer%20Blank_zpsww30de1i.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Reamer%20Blank_zpsww30de1i.jpg.html)

If you look closely at the section immediately aft of the pilot section, you will see a step down in diameter, and then a taper where the diameter increases at a 1* angle (per side) until the taper meets the parallel chamber portion, which is 0.006" larger than the pilot diameter.... Of that tapered portion, the first half, right behind the pilot, never touches the barrel.... As the reamer progresses into the breech end of the barrel, the pilot centers the reamer, and eventually the tapered part starts shaving away the lands until they are gone.... At that point, the parallel portion of the reamer enters the bore, and the chamber gets longer, and the leade moves forward in the bore, until you stop machining.... In my case, I will be stopping when the transition between the leade and the chamber is about 1/8" forward of the front of the barrel port.... The exact chamber depth will be determined by when the base of the bullet stops at that point.... with the nose of the bullet partially engaged on, and centered by, the tapered leade.... I want to be able to chamber the bullet easily, yet have the nose started into the rifling....

The next step was to mill the flutes.... I mounted the reamer blank in a 3/8" 5C Collet in a hexagonal holder, and then mounted the holded in the milling attachment on my lathe.... I have a stop on the vice so that I can remove and replace the holder, indexing it 120* each time to get three evenly spaced flutes.... Each flute consists of a milled slot from just behind the pilot to just behind the chamber portion, ending in the shank.... The end of the mill is stopped a few thou past the centerline, so that the angle between the cutting face and the tangent to the circle at that point is just a bit less than 90*.... If you stop right at the center, at 90* to the circle, you get a very smooth cut but extremely slow cutting.... The further you go past the center, the more acute the angle, and the more aggressive the cut.... I use about 0.010" past center on a .30 cal, so on this smaller reamer I used only 0.006" past center for the end of the mill.... The cuts are made up from the bottom of the blank, removing only 0.010" at a time with a 1/8" end mill, using conventional milling, not climb cutting (ie always cutting so that the flutes of the mill are digging into the work as you feed it into the end mill).... I made 5 cuts, so the flutes are 0.050" deep.... Here is a photo of the reamer in the Collet, after the flutes have been cut....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Reamer%20Flutes_zpsgyhoqm3r.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Reamer%20Flutes_zpsgyhoqm3r.jpg.html)

Notice that the flute starts aft of the pilot, at a diameter smaller than the pilot, and in the first half tapers larger in diameter until it reaches the diameter of the chamber, and then straight back to create the parallel chamber.... At the very back, it ends just behind the beginning of the reduced diameter shank.... There are three identical flutes, spaced 120* apart around the reamer.... The next step is to make sure the cutting edges are clean of burrs, and then harden the reamer by heating to Cherry red and quenching in oil.... That is followed by a final polish and tempering in an oven to give the reamer the right balance of hardness and toughness.... It is my plan to show those steps in the next post, assuming I get them done tomorrow....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 17, 2016, 12:04:51 PM
Here is the hardening process.... I like using a slow running drill press (mine is ~300 rpm) so that I can heat the reamer evenly.... You don't want to clamp too much in the chuck, to minimize heat loss.... Carefully clean the reamer to remove any oil or grease, and then rub it all over with a bar of soap.... I use Ivory.... If you neglect this step, after hardening it will be coated with a black scale that is hard to remove.... The coating of soap will leave it a dull grey after you wash off the scale.... The jar of oil underneath is simply Canola cooking oil, which works fine for the quenching....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Hardening_zps60s5ddqb.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Hardening_zps60s5ddqb.jpg.html)

With the drill press running, you need to heat the reamer red hot, including part of the larger stub, which acts like a reservoir to hold some of the heat.... If you don't it may cool too quickly and not get hardened evenly.... I didn't have it quite hot enough when I took the photo below, so reheated before quenching.... If you are using an acetylene torch instead of propane, don't get the inner flame cone too close, it is hot enough to melt the steel (the cutting edges will melt first!) and ruin all your machine work.... You have to heat it to a nice glowing red, at which temperature, steel loses its magnetic properties.... You can test that with a magnet if you want, to make sure it is hot enough.... If it is, the magnet will not be attracted to it at all....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Heated%20Red_zpsrdfcek7v.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Heated%20Red_zpsrdfcek7v.jpg.html)

Hold it at this temperature for 20-60 seconds (bigger reamers need longer) to make sure that the temperature is even throughout, and then quench it quickly in the oil.... Make sure you plunge it past the shoulder, so that the entire reamer gets hardened.... In the photo below (taken after) is it not quite deep enough....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Quenching_zpshuasvbjw.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Quenching_zpshuasvbjw.jpg.html)

Leave it rotating in the oil for about a minute, and then raise it back up.... CAUTION, IT WILL STILL BE HOT ENOUGH TO BURN YOU !!! .... It will be a horrible looking, black, scaly mess, but once cool enough to handle most of that will come off easily.... If you missed a spot with the soap, you will know, because there will be a piece of black scale that has to be sanded off.... At this stage, the steel will be extremely hard and brittle, like glass.... You will NOT be able to scratch it with a file if it is properly hardened.... Do NOT drop in on a concrete floor, as it could shatter.... Obviously, that is no good for our purposes, so we will have to temper it.... I will cover that in the next post....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 17, 2016, 01:14:08 PM
After hardening, I removed all the scale and repolished the reamer.... It looked like this....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Polished_zpsjebzajhy.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Polished_zpsjebzajhy.jpg.html)

You will note that while I spun it in the lathe to polish the pilot and shank (and the large stub), I polished the actual leade and chamber reamer lengthwise, just removing the scale.... I didn't want to make it smaller, or dull the cutting edges.... After polishing I then used my wife's oven, set at 480*F, to temper it for an hour.... This changes the molecular structure slightly, making the reamer tougher but not as hard.... After tempering and cooling, it looked like this....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Tempered_zps70dycpwr.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Tempered_zps70dycpwr.jpg.html)

The hardness of the part can be judged somewhat by the colour after tempering.... Using 480*F, which is recommended for reamers, should result in a "dark straw" colour.... but realistically, you may see anything between straw and brown.... The mottling on the reamer portion is not a result of uneven tempering, but rather of incomplete polishing, which realistically won't matter.... All that remains is to carefully hone the cutting edges on the radial surface (the part cut by the end of the mill).... In the upper photo, that is the upper flat portion, that the barrel is rotating TOWARDS....  Do NOT touch the circumference, other than to brush it lightly with 600 grit to remove any microscopic burrs from the honing, or you could make it smaller, and then it would cut the chamber undersize.... If when you go to use the reamer you find it cuts too slowly, you can lightly stone the TRAILING edge of the flute OPPOSITE to the cutting edge, putting a very slight bevel on it.... GO SLOW, as this can change the cutting rate very quickly.... That is the edge in the center of the reamer the upper photo....

Bob

Title: Re: Regulated Disco Double
Post by: rsterne on December 17, 2016, 05:13:42 PM
Here is the process of machining the chamber.... Ready to start cutting.... I centered the tailstock using two 60* centers, and then used the pilot of the reamer as a reference to center the breech of the barrel in the 4-jaw chuck.... I had preciously faced off the breech square.... Note the cutting oil in the bore, and in the channel of the reamer.... I put one channel at the top as an oil reservoir.... I had already advanced the reamer until it just touched, you can see the shiny mark about 1/3 of the way along the flute where the taper started to touch the rifling, before I took this photo.... I cut at the slowest speed on my lathe, which is 28 RPM....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Ready%20to%20Start_zpsfdq5ssqu.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Ready%20to%20Start_zpsfdq5ssqu.jpg.html)

Once the leade section of the reamer starts to cut, I slowly advance the reamer in stages of about 0.008" (1/12 turn of the tailstock handwheel) and allow two full revolutions of the lathe before continuing.... Every half turn of the handwheel (0.050"), I remove the reamer and clean it and blow any chips out of the bore and add more oil.... The chips are nothing more than metal dust that turns the oil black, they are that fine.... In the photo below, the leade portion of the reamer has already entered the bore, and the parallel chamber section is about to enter....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Starting%20Chamber_zpsll0lfua2.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Starting%20Chamber_zpsll0lfua2.jpg.html)

In the next photo, the flutes are fully inside the barrel.... It is at this point the maximum load has been reached.... If you continue to be careful, you can breathe a sign of relief, the reamer didn't break off inside the bore.... At some point, usually before this point, I have already withdrawn the reamer and chambered a bullet until the nose touches the leade.... By careful measuring you can figure out how deep you need to go.... On this reamer, I am now in 1.10" from the front of the pilot, but the front of the parallel chamber is only inside by 0.40".... I need the back of the bullet even with the front of the TP hole in the receiver, which is 0.50" from the back of the barrel.... From this point on, I use up quite a few bullets in measuring my progress by chambering them, using the end of the pilot on the reamer as the nose of the bolt, and then pushing them back out from the muzzle with a cleaning rod to examine them with a magnifying lense.... This allows you to measure how far to the back of the bullet by counting turns on the tailstock handwheel....Mine is 0.100" per turn, which makes it easy.... Alternately, you can measure from the breech to the back of the bullet directly with the depth pin on calipers....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Maximum%20Load_zpsux4lmtj0.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Maximum%20Load_zpsux4lmtj0.jpg.html)

I ended up needing exactly two more turns to have the nose of the bullet nicely engaged in the leade, yet have no rifling marks on the drive band, when the back of the bullet is 0.50" inside the barrel.... The photo below shows the position of the reamer at full chamber depth....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Full%20Depth_zpsxy04mmle.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Full%20Depth_zpsxy04mmle.jpg.html)

Basically the chamber is now done.... It turned out that my reamer was slightly undersize in the chamber portion, and bullets sized to 0.217" (the groove diameter) were slightly tight, and picking up marks from the chamber.... I used a piece of 3/16" brass rod with a split in the end, and a bit of 220 grit sandpaper in it, to polish the chamber out another thou so that a bullet sized to the groove diameter loaded smoothly.... If you are going to err on the reamer, better too small than too big, you can always polish the chamber out to the perfect diameter.... Here is a photo of the reamer after use....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Reeamer%20After%20Use_zpsgc1frer6.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Reeamer%20After%20Use_zpsgc1frer6.jpg.html)

You will notice the major wear mark in the center of the flute, that is the portion of the leade that machines off the rifling as you advance the reamer into the barrel.... Behind that are some smaller wear marks where the reamer is rubbing inside the parallel chamber as it advances.... Here is a photo of a bullet and some pellets after chambering so that the back of it is 0.50" from the breech (ie level with the front of the barrel port)....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Succesful%20Chamber_zpsrsp1z5ji.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Succesful%20Chamber_zpsrsp1z5ji.jpg.html)

The top row are JSB Exact pellets.... on the left an 18gr. Heavy, in the middle a 25 gr. Monster, and on the right the new 34 gr. Beast.... You will notice the rifling marks on the head band of each pellet, but the only marks on the skirt are where it has collapsed slightly because skirts are always oversized.... The bullets in the bottom row are the new 30 gr. BBT.... On the left is a bullet sized to 0.217" but unchambered.... while the one on the right has been chambered and then pushed back out.... You can clearly see the rifling marks on the back of the nose where it has engaged about halfway along the leade.... but there are no marks on the drive band (sorry for the glare of the flash).... The parallel chamber ends (and the tapered leade starts) just forward of the front of the rear drive band.... The bullet chambers easily just pushed into the breech by hand with a 3/16" brass rod.... You can feel it engage the leade in the last 1/10" of travel.... Anyway, that is how you chamber a barrel.... As you can see, a chamber properly designed and machined for bullets can easily accept waisted pellets....

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 18, 2016, 07:53:39 AM
Now we are ready for some accuracy pics.  Nice work, Bob.

Joe
Title: Re: Regulated Disco Double
Post by: oldpro on December 18, 2016, 09:05:34 AM
 Serious time involved but will be very rewarding in the end.
Title: Re: Regulated Disco Double
Post by: rsterne on December 18, 2016, 10:14:53 AM
I have had a few questions about the flutes on the reamer.... Here is a sketch of the end view.... This drawing is for a conventional lathe, running forward, with the reamer in the tailstock, and viewed looking towards the headstock.... The reamer in this application is fixed, and the barrel is rotating counter-clockwise around the drawing.... The short edges of the flute cutouts are the cutting edges....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Reamer_zpsywtq5w0p.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Reamer_zpsywtq5w0p.jpg.html)

This is a generic drawing, where 1.000 is the maximum diameter of the reamer.... The flute cutouts which are milled out are shown in blue.... The short edge is where the end of the mill cut.... the long edge is where the side of the mill cut.... For three flutes, I would not go past 1/2 the radius of the reamer with the side of the mill, or you will weaken it too much.... The end of the mill stops anywhere between the centerline and about 5% of the diameter past the centerline (I have never tried more than that).... The further you go past the centerline, the faster the reamer cuts, but the rougher the finish.... If you use three flutes, they are 120* apart.... You can also make a single flute reamer, the cutout is shown as the dotted blue line.... You basically remove a 90* segment of the circle, and again, taking the end of the mill just past the centerline increases the speed of cut....

I offer no guarantees that you will find this design acceptable.... but I have used a few single flute reamers successfully (but I did break one).... and I made and used my first three point one on this build without issue.... I had my cutting edge only 2.5% below the centerline, and it cut very slowly, the chips were basically just metal dust.... On the other hand, having broken a reamer once, inside a barrel, I was being VERY careful.... I make mine from O-1 Drill Rod, which is hardened after machining by heating red hot and quenching in oil.... The reamer should then be tempered at 480*F, which should result in a dark straw to brown colour....

Bob

Title: Re: Regulated Disco Double
Post by: tkerrigan on December 18, 2016, 07:48:02 PM
Thanks Bob, now I fully understand.  Regards, Tom
Title: Re: Regulated Disco Double
Post by: rsterne on December 19, 2016, 07:38:17 PM
Today I finished up the breech end of the barrel.... First of all I "Indexed" the barrel.... Not by shooting it and determining the smallest groups, which is the proper way, but by chucking the breech portion in my lathe and using a dial indicator at the muzzle, I determined which way the barrel "droops", and marked which side would be the bottom so that when installed in the breech the muzzle would be at it's lowest point (6 o'clock).... This has been shown over the years to produce the tightest groups, with the second best groups occurring when the barrel bend is towards the top (12"o'clock).... Barrels tend to straighten out when fired, so if the bend is to the side, not only do the groups tend to be larger, they tend to be wider than high.... With the bend in the barrel in the vertical plane, you have more chance of using a barrel tuner (adjustable weight) to shrink the group size.... Having the bend upwards would help the bullet path intersect the scope centerline better, but I opted for the bottom as 90% of the people who bother to index their barrels prefer that.... Tensioned barrels tend to be less sensitive to barrel indexing, but I decided to do everything I could for accuracy....

Once I knew "which way was up", then I knew where to machine the barrel port, so that was the first job.... I measured the distance from the front of the magazine cutout to the center of the TP hole in the breech, added 1/16" to allow for the barrel protrusion that the MRod magazine needs to clip onto, set the barrel up in my milling attachment, and using an edge finder laid out the exact center of the bottom of the barrel, the correct distance from the breech end and drilled a center hole.... I then enlarged that with a 5/32" mill, and using a 5/16" mill made the spot face where the transfer port will seal.... I then used a 7/32" mill, which is the same diameter as the ID of the transfer port I will be using (and the valve exhaust port) and made a shallow mark in the spot face where the transfer port ID will be.... I changed back to the 5/32" mill, moved the barrel forward 1/32", and plunged the mill back in to make the back of the oblong barrel port.... I then rotated the milling attachment 30* so that I could machine the forward sloping front part of the barrel port.... I carefully positioned the 5/32" mill so that it just tickled the front of the 7/32" ID mark, and milled down until I hit the bore.... This made the barrel port 0.160" wide by 0.270" long, with the back vertical and the front sloping forward from the TP into the bore.... This gives me a barrel port that is the same area as the bore, but only 75% as wide, so that the pellets/bullets will not be damaged when loading.... I then used a 60* countersink to blend the 7/32" hole at the spot face into the 0.16 x 0.27" barrel port, removed the barrel from the lathe, and finished the job up with a small spherical diamond burr in my Dremel.... The result is a smooth transition from the 7/32" barrel port to an oblong, bore area, barrel port....

I then loosely installed the barrel in the receiver, using an MRod magazine to hold the back end in the right location in the magazine notch, and the 5/16" spot face lined up perfectly with the TP hole in the receiver.... I loosely installed the 8 setscrews that will hold the barrel in place, tightening them only enough to put small marks in the barrel.... I then pulled the barrel, mounted it back in the milling attachment, using a 5C Collet in a square holder (against an end stop), and adjusted it until the spot face for the barrel port was perfectly centered.... I then moved the barrel in 3/4", and using a center drill put a witness mark on the barrel, to make sure it lined up perfectly with the setscrew mark, and another one 3/4" further in again.... The two rows of setscrew holes in the receiver are 3/4" and 1-1/2" forward of the transfer port, and on all four sides, 90* apart.... With the barrel in the square collet holder, I could rotate it 90*, and repeat this process, and prove to myself that the shallow holes I was about to drill in the barrel would be where the setscrews were.... Everything looked OK, so I used a 3/16" stub drill and drilled eight 0.030" deep pockets in the barrel for the setscrews to tighten into.... This will prevent the cup-point screws from raising rings on the barrel surface which would damage the inside of the receiver, and can actually jam the barrel into it.... You MUST have spot holes or flats for this reason.... In addition, with my tensioned barrel, I wanted all the screws to carry equal load, and the shallow pockets will mean the side of the setscrew point will be against the pocket, instead of just relying on friction from the ring of the cup point.... This will mean that they will easily share the load of up to 1300 lbs. of tension on the barrel from the Bellevilles at the muzzle....

I reinstalled the barrel, lined up the transfer port and magazine again, and lightly tightened the 8 setscrews into the pockets.... On removing the barrel, I found that the two circular marks from the lower cup-point setscrews were perfectly centered in the pockets, but the other six were to one side or the other (although perfectly centered fore and aft).... I used that small round burr again, and ground off the marks from the setscrews in the other 6 locations.... This moved the recess over towards the point of contact with the end of the setscrew, which would allow it to tighten slightly more on the next trial.... After repeating this procedure a few times, I got completely round, centered rings from the cup-points on all 8 setscrews when they were tightened up.... This means that I don't have to crank a crazy amount of tension into them, which could distort the bore.... but that they will all share in the tension load on the barrel.... It took a bit of extra time, but produce a wonderful result that I have 100% confidence in.... You can see the pocket for the setscrews, and the nicely centered marks from the setscrews, in the photo below....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Porting%20and%20O-ring_zpsp3ahsefk.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Porting%20and%20O-ring_zpsp3ahsefk.jpg.html)

The last job was to machine the groove for the internal O-ring that seals the bolt.... Before I could do that I had to finish turning down the nose of the bolt so that it fit nicely in the chamber I reamed in the barrel.... I had left it oversize for this purpose.... I usually have problems getting a good fit between the bolt and the barrel, because I always seem to have a slight misalignment of the 1/2" holes in the front and back of the receiver.... but I knew this was the most accurate breech I have made to date, and I was not disappointed.... Once I got a nice sliding fit between the bolt nose and the barrel chamber, I put them both in the receiver, and the bolt functioned well.... I could feel a slight resistance from the bolt touching the inside of the barrel, and there is a shiny mark on one side, but it worked without having to sand one side of the bolt or turn it down smaller, so I was delighted.... I dragged out the specially ground tool I have for making O-ring grooves, it is shown in the above photo.... It allows me to machine a 0.070" wide groove inside the barrel, about 0.040" from the end, to hold the O-ring, in this case a #009.... I slowly increased the depth of the groove until it was 0.060", tried the O-ring and found it wouldn't quite go in place, so I deepened the groove until it would JUST lie flat in the groove.... I tried the bolt, and it slid smoothly through the O-ring.... There is 0.007" of compression on each side of the O-ring with the bolt in place, so I think it will seal fine.... if not, I can always use a 90D O-ring instead of the 70D I tried today....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 20, 2016, 06:22:13 PM
I seems to take forever to get all the last little details done on a custom PCP project.... Today's job was to make and install the cocking pin in the bolt and cut the recess for it in the bottom of the receiver.... It took me all afternoon.... The hardest job was to figure out the exact spot it had to go.... The angle relative to the bolt handle was the easy part.... Too far forward the slot for the bolt handle was too short, and the handle would hit the end before the hammer cocked.... Too far aft, and the nose of the bolt wouldn't withdraw far enough to allow me to remove the magazine.... Yeah, I should have made the slot 1/16" longer, but that is a difficult thing to set up to machine once, let alone change it later.... Anyway, I finally figured out where to drill and tap the bolt for the cocking pin, and I tapped it 6-32, with a small flat for the head of the SHCS to tighten against.... Since I originally machined the cocking slot in the receiver with a 3/16" mill, I had to use a 7/32" mill to make it wider for the head of the 6-32 screw.... Once I did that, it slid back and forth fine, but the head didn't stick down far enough to properly engage the cocking pin in the hammer.... Well, it caught it, but only right at the top, which with a strong hammer spring can bend the pin, so I had to make a longer cocking pin for the bolt.... I did that by using Loctite 638 (green) to install a hex nut tight against the screw head, and then turned it down to the same diameter as the screw head.... That caused me more grief, because it was so long I barely had room to make the recess in the bottom of the receiver to clear it when it rotates sideways when you close the bolt without breaking through the side of the receiver.... Yeah, one change becomes two, then four, nothing is as simple as it seems....

Anyway, I laid out and milled the recess in the bottom of the receiver to allow the cocking pin to rotate to the side and pull back when the bolt handle is withdrawn into the J-Slot.... Again, that took multiple passes to give enough clearance without carving away more of the 1/2" diameter bolt channel than I need to.... I had to finish it up by hand, using a spherical burr in my Dremel to get the last bit of clearance for the corner of the head of the cocking pin screw.... Once finished, I tried it and it cocks the gun smoothly, so the day was a success.... Here is a photo of the receiver with the recess and the completed bolt....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Cocking%20Pin%20and%20Recess_zpsyz1ohvqw.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Cocking%20Pin%20and%20Recess_zpsyz1ohvqw.jpg.html)

You can see there isn't much metal left in the receiver beside the recess, and it's actually a bit thinner than what you see down inside at the height of the corner of the rotated cocking pin where I had to clearance it by hand.... However, the job is done, and I'm closing in on getting ready to fire the first shot....

Bob
Title: Re: Regulated Disco Double
Post by: oldpro on December 21, 2016, 08:57:37 AM
What are ypu using to cut the concave channel on the reciever?
Title: Re: Regulated Disco Double
Post by: rsterne on December 21, 2016, 09:28:36 AM
A 7/8" ball end mill.... However, carbide router bits also work fine on aluminum.... and way cheaper....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 21, 2016, 03:09:14 PM
Well, today was the day!.... I spent the morning doing the final barrel prep work.... I crowned the muzzle, lapped the bore with JS Bore Paste, and then followed that by a polish with JB Bore Brite.... It now gleams from end to end.... I then installed it into the receiver and installed the bolt.... I slid on the front breech retaining band, and installed the PRod trigger group, then slid the hammer into place and installed my borrowed SSG assembly, which I set to minimum gap.... The last step was to measure the length required for the transfer port, and make one from a piece of 5/16" Teflon rod.... I drilled it out to 7/32", and carefully faced the end off until it was 0.010" longer than the space, so it would have a bit of "crush" to seal properly.... Bolting down the receiver was the last task before firing the first shot.... Well, except to take a photo....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/First%20Assembly_zpsfe8lc9ll.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/First%20Assembly_zpsfe8lc9ll.jpg.html)

As you can see, I haven't fitted the shroud, or modded the stock yet, those items will come after initial testing and tuning.... The gauge said the regulator setpoint was 1900 psi, so I loaded up a magazine, and tried the 34 gr. JSB Beasts....They fed fine, and the first shot was 867 fps (57 FPE).... Not bad for 1900 psi.... I shot a few of each weight pellet, and then shot the 25.3 gr. Monsters until the velocity started to change, and it actually went up about 20 fps at just under 1800 psi, so the setpoint is a bit lower than the gauge reads (or vice versa).... With the pressure a couple of hundred psi below the setpoint, I was able to increase the regulator adjustment, I turned the screw about 45* CCW, and refilled the lower reservoir.... The gauge now read nearly 2200 psi, so I repeated the procedure with the higher setpoint.... Here are the initial results.... The 18.1 and 25.3 gr. are JSB Heavies and Monsters.... the 27.4 and 29.6 gr. are my new BBT HP and FN cast bullets.... and the 34.1 gr. are the new JSB Beasts....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Disco%20Double%20Reg22%20First%20Test_zpszjtthl6h.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Disco%20Double%20Reg22%20First%20Test_zpszjtthl6h.jpg.html)

As you can see, the 18.1 gr. JSB Heavies were Supersonic, accompanied by the typical loud CRACK!!!.... The were the only pellet that shot faster at 2100 psi than at 1800, which tells me that I don't have enough hammer strike at the higher pressure.... Since I am out of adjustment with the QB spring (it is right at coil bind with no gap), I will need to come up with a different spring combination, or forego the SSG and just use the QB spring in a conventional preloaded arrangement for now.... I think I will do the latter, at least until I can establish what the maximum velocities are with the various pellets at the current setpoint.... The BBTs, both HP and FN, exceeded 60 FPE at 1800 psi, and the 25.3 gr Monsters were very close to that.... and it would seem that there is more there if I increase the hammer strike.... That certainly means that the gun is breathing well, with the bore-size porting.... Those are pretty healthy FPE numbers at such a low pressure, so I'm encouraged.... and I'm looking forward to finding out what the limit is at the ~2100 psi setpoint once I add some more hammer strike to find out where the plateau is with the different pellet weights....

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 21, 2016, 05:25:14 PM
Cool, Bob. 
Title: Re: Regulated Disco Double
Post by: Christopher on December 22, 2016, 05:42:25 PM
Wow, impressive at that pressure. Seems mighty nice to simply get your screwdriver and adjust the regulator then right back to shooting instead of having to degas the gun. Thanks for all the details of your build along thread. Another spectacular job. Looking forward to the results with more hammer strike.

Chris
Title: Re: Regulated Disco Double
Post by: rsterne on December 22, 2016, 05:48:39 PM
As long as the pressure in both upper and lower tubes is LESS than the LOWEST pressure the regulator will be set at.... by, say 200 psi to give you some room fore error.... you can adjust the regulator without completely degassing the gun.... If you are increasing the pressure there is less danger of damaging the regulator than if you are decreasing the setpoint pressure.... because to decrease the setpoint you have to screw the adjustment (seat) clockwise which is towards the piston.... You don't want to be turning the seat when it is pressing against the end of the piston where the HP seal is located.... as it could damage the seal....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 23, 2016, 02:09:28 PM
I tried four different pressures, each 1/4 turn apart on the regulator adjusting screw, and at each pressure I started at zero gap on the SSG and then increased the gap a turn at a time until the velocity dropped below 600 fps at each pressure.... I then plotted the velocity vs. gap at each pressure, with the following results....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/DD%20Reg22%20Velocity%20vs%20Gap_zpsykqidub7.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/DD%20Reg22%20Velocity%20vs%20Gap_zpsykqidub7.jpg.html)

The regulator setpoint dropped about 450 psi for 1/4 turn from 2150 down to 1700, then another 450 down to 1250, and then 350 psi from there for the last 1/4 turn, down to 900 psi.... At the highest pressure, even at zero gap, there is not enough hammer strike to reach the velocity plateau.... At 1700 psi, it is just about on the plateau at zero gap.... In both cases the maximum velocity was supersonic with the 18.1 gr. JSB Heavies.... Breaking Mach 1 on only 1700 psi is pretty impressive....  :o

At 1700 psi, the plateau appears to be at about 1150 fps,  the knee of the curve was at about 1-2 turns of gap, and the downslope started at about 3 turns out at ~1000 fps.... At 1250 psi, the plateau was 1051 fps, and the knee of the curve occurred at 3-4 turns of gap, with the downslope starting at about 5 turns out at ~900 fps.... With the pressure at 900 psi, the plateau was 956 fps (37 FPE), the knee occurred at about 5 turns of gap, and the downslope began at about 6 turns of gap, at ~800 fps....

The regulator is very easy to adjust, and 100 psi increments should be relatively easy to obtain.... From 1250 to 2150 psi was 1/2 turn of adjustment, so each "hour" on a clock face would be about 150 psi.... That works out to about 50 psi for each 10 degrees.... The regulator seemed to have good stability, returning to the same setpoint after each shot, as close as I can read the gauge, which is a 3000 psi, 180* sweep, 5% gauge, with 200 psi increments.... I am delighted with the performance of the regulator.... and equally pleased with the ability of this gun to reach 950 fps with 18.1 gr. JSB Heavies at only 900 psi....

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 23, 2016, 05:11:13 PM
Seems like you have it about summed up, Bob.

Joe
Title: Re: Regulated Disco Double
Post by: rsterne on December 23, 2016, 06:20:56 PM
I reset the regulator to 1150 psi, filled to 2000 psi, and shot 10 shots with the 18.1 gr. JSB Heavies with 3 turn of gap on the SSG and recorded the pressure drop.... I then repeated that at 4, 5, and 6 turns of gap, with the following results....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/DD%20Reg22%201150%20psi_zpsula0jocy.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/DD%20Reg22%201150%20psi_zpsula0jocy.jpg.html)

At 3 turns, the average velocity was 1018 fps (42.4 FPE) at an efficiency of 1.28 FPE/CI.... At 4 turns of gap, the average velocity was 1003 fps (40.5 FPE) at 1.43 FPE/CI.... With the gap increased to 5 turns, the velocity averaged 960 fps (37.1 FPE) at 1.64 FPE/CI.... and at 6 turns the average was 844 fps (28.6 FPE) at 1.95 FPE/CI.... Remember, this is at only 1150 psi.... The ES over the 10 shots was around 14-15 fps for most strings, although for the one at 4T out it was only 7 fps (0.7%).... Typically SSGs have a narrower ES when the preload is set so that the gap is small (0.020-0.060"), but I didn't bother reducing the preload before shooting these strings, so the gap at 6T out was actually over 1/4".... (over 1/3 of the hammer travel wasted)....

I then filled the gun to 2900 psi (my Great White needs filling), and shot an entire string with the gun adjusted for 38 FPE (an average velocity of 972 fps with the 181 gr. JSBs).... I stopped when the first shot dropped below 950 fps, which occurred at shot 45.... Yep, that's a total of over 1700 FPE on a single fill.... Here is the string....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/DD%20Reg22%2018%20gr%20String_zpsc7d1qrob.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/DD%20Reg22%2018%20gr%20String_zpsc7d1qrob.jpg.html)

The ES wasn't great, about 2% with unsorted pellets and the large gap in the SSG.... You can see what happens to the pressure curve at the regulator setpoint of 1150 psi, the slope decreases because both tubes are dropping in pressure below that.... I got 35 shots from 2900 psi to the setpoint, another 5 below that down to 1000 psi.... and another 5 shots before the declining velocity opened the ES up to 4%.... The overall efficiency over the 45 shots was 1.44 FPE/CI, down a bit from the results above at 37 FPE.... so I appear to be right in that area where a slight change in gap and velocity makes a big difference in efficiency.... If I were really interested in tuning for these pellets, I would use less preload on the hammer spring and reduce the gap in the SSG to make the gun easier to cock.... I would expect that to narrow the ES and increase the efficiency as well....

This completes my testing of the regulator, now it's time to change out the SSG for a conventional preloaded spring (temporarily) so that I can crank the power up with heavier bullets and see just what this gun is really capable of.... 

Bob
Title: Re: Regulated Disco Double
Post by: Christopher on December 24, 2016, 01:10:45 PM
I scanned back through this thread and looked for barrel length and didn't see it. Probably just missed it, but how long is the barrel?

Outstanding results.....

Thanks,
Chris
Title: Re: Regulated Disco Double
Post by: rsterne on December 24, 2016, 02:20:13 PM
Time to get down to business tuning this gun the way I wanted it in the first place.... The SSG using the QB spring did not have quite enough power, so I replaced it with a conventional RVA using the same spring but with preload.... In addition, I added a lightweight sliding spring guide as a valve lift indicator, so that I could make direct measurements of the valve lift at various preload settings.... Here is the SSG (lower) and the Lift Measuring Rod for comparison....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Lift%20Rod%20and%20SSG_zpsj3e24ohf.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Lift%20Rod%20and%20SSG_zpsj3e24ohf.jpg.html)

The same spring (from a QB) is used in both, so you can see how much preload I have in the SSG.... Conversely, you can see that with the preloaded setup, the spring will still be pushing the valve open throughout the entire shot cycle.... The Lift Measuring Rod is just a piece of 3/16" K&S aluminum tubing with a short flathead 8-32 screw in the end.... the head of the screw ends up captured between the spring and the hammer, so the tubing slides with the hammer.... There is a #008 O-ring on the end, which you push up against the RVA adjusting screw, then cock and fire the gun.... Since the tube travels with the hammer, the O-ring slides back along the tube the same distance the valve opens.... so the distance between the RVA screw and the O-ring is the same as the valve lift....

The regulator pressure was still sitting at 2000 psi, within as close as I could measure it, so the regulator seems to have settled down nicely and is now showing no signs of creep overnight.... When it was brand new, it was gaining about 100 psi overnight, and it is not unusual to see a short "break-in" period like this.... I filled the lower reservoir to 3000 psi, cranked the preload to maximum (coil bind), loaded the magazine with the new 34 gr. JSB Beasts, and fired 3 shots across the Chrony.... The velocities were 1006, 997, and 997 fps, and it used 1000 psi for the three 75 FPE shots.... Incidently, 75 FPE is exactly what my Spreadsheet predicted for my "lofty goal" with a 24" barrel at 2000 psi.... The barrel on this gun (although I ordered a 25") is 28" long, so that is 100% consistent with my expectations.... to fall short of the spreadsheet prediction by a small amount.... I measured the valve lift, and the O-ring gap was 0.200", which is all the travel the valve stem has before being driven flush with the back of the valve, so I had all the hammer strike I can possibly use (and more than I need).... I turned the RVA out 1 turn, shot another 3 shots, recorded the velocity, pressure drop for 3 shots, and valve lift, and continued doing that until the velocity dropped below 600 fps.... Here are the results....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/DD%20Reg22%20Velocity%20vs%20Preload_zps3lfhsuwv.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/DD%20Reg22%20Velocity%20vs%20Preload_zps3lfhsuwv.jpg.html)

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/DD%20Reg22%20Lift%20vs%20Preload_zpsvranjrkd.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/DD%20Reg22%20Lift%20vs%20Preload_zpsvranjrkd.jpg.html)

There is a LOT of useful information in those two charts.... First of all, the velocity plateau, which is at 997 fps, starts when the preload is backed out 6 turns (1/4") from coil bind, and in fact there is no real drop in velocity for the next couple of turns.... At 6 turns out, the pressure dropped 580 psi for 3 shots averaging 994 fps.... but at 8 turns out, the pressure dropped only 400 psi for 3 shots averaging 983 fps.... At 9 turns out, the pressure only dropped 320 psi for 3 shots averaging 963 fps.... In that 3 turns of adjustment, I lost 3% in velocity and used 45% less air.... and the efficiency increased from 0.74 FPE/CI to 1.25 FPE/CI.... Compared to maximum preload, when the hammer was hitting the back of the valve, it is only using 1/3rd of the air.... So 9 turns out is clearly the "knee" of the curve, with the downslope starting at 10 turns out.... You will also notice that until the preload was backed off 2 turns from coil bound, the lift stayed constant at 0.20" because that was the maximum the valve could physically open.... At 6 turns out, where the velocity just starts to drop, the lift is down to 0.14", and at 9 turns out, at the knee of the curve, it is just 0.10".... It is that decrease in lift, and its associated decrease in dwell, that decreases the amount of air released by the valve.... Since the throat of the valve is 0.266", driving the valve more than half that distance open gains nothing in power, it just wastes air.... I have seen this many times before, and now believe it to be a good rule of thumb for how much you need to allow the valve to open.... If it can physically open more than half the throat diameter, that's all you need to allow for.... That means that shortening the valve stem can allow for more useful hammer stroke, which can then reduce the cocking effort.... I may in fact drill a recess in the front of my hammer to allow another 0.050" of hammer stroke.... That should have NO impact on the maximum power, I should still be able to reach the plateau, even with the 34 gr. pellets....

I haven't yet shot a full string with the 34 gr., but based on these tests I should be able to get one 10-shot magazine at 960 fps (70 FPE) by the time the pressure drops to the 2000 psi setpoint.... and that was my goal.... In fact, when I started, I planned on using a PRod magazine, and they are only 8 shots.... but at that time I was unsure if I could get enough power at 2000 psi, and thought I might have to use 2200 for my setpoint.... I did fire a few shots with my 30 gr. BBT, and at 9 turns out the velocity was 1023 fps, dropping to right around 1000 fps at 10 turns out, so logically I should be able to get more than 1 full mag. with the BBTs.... One other thing I should mention, there is a BIG decrease in the report when you hit the knee of the curve, which is to be expected....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 24, 2016, 05:18:32 PM
I milled a 3/16" diameter recess in the front of the hammer that is 0.050" deep to increase the hammer travel to 0.75".... Without changing the preload I gained about 20 fps at the 10T out position.... This is because the cocked force is the same but the uncocked force is less, dropping the average spring force slightly while increasing the travel distance.... This slightly increases the hammer strike without any increase in cocking force.... I shot a 10 shot string at that setting, and it had not dropped below the setpoint, proving the gun is capable of doing that with the 34 gr. JSB Beasts in the mid 900s on a 3000 psi fill....

I then shot a few shots with my 29.6 gr. BBT FN bullets at each preload from 10 to 12 turns out.... It was nearly 1000 fps at 10 turns, and just under 900 fps at 12 turns.... so that determined that 11 to 11.5 turns will be the likely setting for the FN bullets in the mid 900s.... It was about 50 fps faster with the 27.4 gr. HPs, so 12 turns out will be quite close for those.... I also shot some short strings with bullets sized at different diameters at 11 1/6 turns out, and got the following average velocities....

0.216" FN .... 972 fps
0.217" FN .... 963 fps
0.218" FN .... 956 fps
0.219" FN .... 956 fps
0.217" HP .... 1007 fps

I was curious what the relationship would be between diameter and velocity, and as expected the smaller bullets shot faster, because of less resistance inside the barrel.... I wondered about why the "as cast" bullets (they are the 0.219") weren't slower, and then I remembered that the chamber is 0.218", and the bullets were noticeably harder to load than the others.... so it was resizing them to 0.218" before they were shot, hence the reason the velocity stayed the same.... The total pressure drop for 10 shots was around 950 psi, so the pressure stayed above the setpoint for all 10 shots, in fact I would expect the 11th shot to not lose any velocity.... not that it matters, because it is a 10 shot magazine....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 26, 2016, 02:26:19 PM
I installed the shroud today, and a scope and bipod.... It weighs 8 lbs. 10 oz. complete, or 8 lbs. even without the Bipod.... Without the scope and rings it is about 6 lbs. 12 oz....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Complete%20on%20Bipod_zpsw6r2opzn.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Complete%20on%20Bipod_zpsw6r2opzn.jpg.html)

I played around with the preload to find a setting that could work for both weights of BBTs and the 34 gr. JSB Beasts.... The RVA ended up at 11.25 turns out from coil bind.... and the gun is quite easy to cock like that.... I then shot some 10-shot strings, refilling to 3000 psi each time.... At the end of the strings it was pretty much right on the 2000 psi setpoint.... so I can shoot one magazine on a fill.... Here is what they look like....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/DD%20Reg22%202000%20psi_zpsa9li4p9l.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/DD%20Reg22%202000%20psi_zpsa9li4p9l.jpg.html)

The 34 gr. JSB Beasts averaged 874 fps (57.9 FPE) at an efficiency of 1.35 FPE/CI.... The 29.6 gr. BBT solids averaged 944 fps (58.6 FPE) at 1.24 FPE/CI.... and the 27.4 gr. BBT HPs averaged 988 fps (59.4 FPE) at 1.21 FPE/CI.... This was using BBTs sized to 0.217".... The ES on the Beasts was just 6 fps (0.7%), and with the BBTs is was just under 2%.... That should prove close enough for shooting out to 100 yards....

I then took the opportunity to see what adjusting the barrel tension does to the group size.... Without the shroud, the 28" barrel was pretty whippy.... It shot OK inside my shop, but the distance is only 20 ft.... Still, I can usually tell if the gun is a shooter or hopeless just during my Chrony sessions at that distance, if I pay attention to aiming.... The JSB pellets were pretty much all 5 touching, but the BBTs ranged from that to a loose 5-shot group you could just cover with a dime.... I installed the shroud, but with no tension on the Bellevilles, just enough to keep the tension adjusting nut from falling off the muzzle.... This did, however, drastically raise the POI, because I had indexed the barrel to the bottom, and it had a noticeable curve to it.... Once I rezeroed the scope, and using the 34 gr. JSB Beasts, I shot a series of 5-shot groups, tightening the nut on the Bellevilles 1/4 turn at a time.... I am using a stack of 5 Bellevilles, and they have a rate of 750 lbs. per 0.010" (singly), so that means each 1/4 turn increased the barrel tension by about 200 lbs.... I stopped at 1.5 turns, which would be about 1200 lbs. of tension in the barrel.... In theory I can go another 1/4 turn without driving the Bellevilles flat, but I don't like to do that, you can ruin them by causing them to take a "set".... I disassembled the stack after tensioning to 1200 lbs., and they had only collapsed less than 0.001" each, so I will use that 1.5 turns as my limit.... Here are the group sizes as I increased the tension with the 34 gr. Beasts....

0 lbs. tension = 0.30"
200 lbs. = 0.44"
400 lbs. = 0.22"
600 lbs. = 0.36"
800 lbs. = 0.19"
1000 lbs. = 0.17"
1200 lbs. = 0.28"

I then repeated the process with the 29.6 gr. BBT FN, sized to 0.217"....

400 lbs. tension = 0.38"
600 lbs. = 0.53"
800 lbs. = 0.48"
1000 lbs. = 0.59"
1200 lbs. = 0.15"

I then tried the 27.4 gr. BBT HP's, also sized to 0.217"....

800 lbs. = 0.45"
1000 lbs. = 0.21"
1200 lbs. = 0.34"

and then at that 1000 lbs. setting I tried other diameters of the HPs....

0.216" = 0.32"
0.217" = 0.21"
0.218" = 0.24"
0219" = 0.25"

I then reduced the tension to 1 turn (800 lbs.) and tried the HPs again....

0.216" = 0.22"
0.217" = 0.45'
0.218" = 0.15"

What I had been told was that once you reached a certain barrel tension, tightening past that point would not decrease the group size.... What I found was that low tensions did not work well, and that I do indeed need about a turn on the Bellevilles (about 800 lbs. of tension) as a minimum.... However, past that minimum, each bullet appears to have it's own optimum tension setting (sweet spot).... and that can change when you change the bullet diameter.... It likely also changes with the velocity.... In fact, anything that changes the dynamic vibrations of the barrel will likely move the sweet spot a bit.... The good news is, that the group size is dramatically reduced by using the tensioned barrel.... I would say that is a 100% success....

Incidently, when I started testing the tension adjustment I found that the POI on the target was walking around in a 6" circle, even at just 20 ft., as I changed the tension.... Since I had drilled only a 1/4" hole in the barrel extension that holds the Bellevilles, I suspected that the pellets were clipping the inside of it.... I removed it and couldn't see any marks inside, but I drilled it out to 9/32" (to provide 1/32" clearance for the pellet) and this went away completely.... There was a slight POI change with tension, as you would expect, but we're talking 1/2" instead of over 10 times that much.... The report is less, with the muzzle blast venting into the shroud, it sounds like a gun where you just backed off the preload a couple of turns.... You can start to hear the ping, but it is certainly not "backyard friendly".... In other words, it made a noticeable, and welcome difference, certainly worth doing if you live where they don't frown on having a quieter airgun.... It seems silly to me that adjusting the power to drop the noise is OK, but venting the air into the shroud and getting the same effect isn't.... It certainly is nothing like what you can achieve with baffles, or a separate LDC.... but it will protect your hearing somewhat, and well worth the 3" increase in length of the shroud....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 27, 2016, 06:50:02 PM
I made a few small changes to the gun today.... I removed the top portion of the rear triple band because it interfered with the scope position.... It now only clamps the two reservoirs together.... The forward band remains the same, with an O-ring supporting the shroud, so that it can move independently of the reservoirs for expansion, but is located to prevent damage if you drop the gun or fall on it.... I call this arrangement "semi-floated".... I added an internal support, just a simple collar that is setscrewed to the barrel, with an O-ring in a groove that is in firm contact with the inside of the shroud, flush with the front of the band that supports the shroud.... That places it 3/7ths of the distance from the receiver to the muzzle, to dampen any harmonics between the tensioned barrel and the shroud.... I also machined twelve marks on the tension adjusting nut, to make a Vernier so that it is easy to ascertain the position of it during tuning the tension.... Every 3rd mark is slightly longer (3, 6, and 9 o'clock), and the 12 o'clock mark is the longest, and marked with black.... There is a corresponding mark on the top of the flange on the CF shroud that doesn't rotate as a reference mark....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Tension%20Vernier_zpsuf9ipnrv.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Tension%20Vernier_zpsuf9ipnrv.jpg.html)

It is the one that was vertical when the nut just touched the Belleville washers, and when tightened one turn puts nearly 800 lbs. of tension in the barrel.... I can tighten at least another half turn from there, and I can record the position as "3 o'clock", or "4:30", or "5:20".... which will make it easy to return to the setting which worked the best.... Each "hour" of rotation is about 65 lbs. of barrel tension.... I haven't yet tested the gun with the intermediate barrel support, and the Motel is booked until after New Years, so it may be a few days before I get the chance.... and even then it will only be at close range inside my shop.... I am hoping the intermediate support will even out the differences between pellets, and allow one tension setting to work for all.... I guess we'll see what happens....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on December 29, 2016, 02:31:25 PM
I burned through another tin of 34.1 gr. JSB Beast pellets today (actually more than a tin), playing with the tension adjustment on the barrel.... I found out that a "1 hour" change (about 65 lbs.) to the tension makes a significant difference to the group size.... but that virtually all the groups are better than previously, since I installed the intermediate support on the barrel.... Having a support between the barrel and shroud at 3/7ths of the distance from receiver to muzzle really settled down the variation in group size as you change the tension, bullet, or velocity....

I increased the velocity with the Beasts to 960 fps (70 FPE), and found that there was a sweet spot just past 1 turn of tension.... Using a 24 hr. clock, starting from zero tension, 1400 hrs. (2 hrs. past 1 turn) gave me the best groups.... Here is an example.... Yes, that is a 34 gr. JSB Beast .22 cal pellet sitting in the hole from a 5-shot group....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/FWB%2034%20gr%2020%20ft_zpsopcyqqcy.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/FWB%2034%20gr%2020%20ft_zpsopcyqqcy.jpg.html)

About half the 5-shot groups at that setting met the "Feinwerkbau Test".... Although I only have 20 ft. available, not the 10M that FWB uses.... I find that when a gun shoots like this inside, if there is a problem at long range, is tends to be the pellet/bullet, not the gun.... At this velocity, I am running right on the knee of the curve at the 2000 psi setpoint with the Beast, it uses 1200 psi for 10 shots, which works out to 1.13 FPE/CI.... I think that is pretty good for a .22 cal at 70 FPE.... With a 3000 psi fill, the last shot (taken below the setpoint) loses about 100 fps, but by filling to 3200 (the gun is safe to at least 3500 psi) the gun is sitting right at the 2000 psi setpoint at the last shot, and the ES is hovering right at 1% (8-10 fps) over the 10 shots....

This is pretty much the kind of tune I was looking for, so I think I'm done with the development of this gun until I can get outside in the Spring to test at longer ranges.... I can chalk this up to another very successful project.... with many thanks to Lloyd Sikes for supplying his new Regulated Disco Double Kit so that I could put it through its paces.... I would highly recommend it for anyone modding a Discovery.... It is capable of a ton of shots at lower pressures, and lots of power when you crank the pressure up.... The external adjustment is easy to use, and covers a wider range than I needed (I used 900-2200 psi during this project).... It can be used with a stock Disco, or one that is highly modified like this one.... I don't see how you can go wrong with it.... Congratulations, Lloyd, on another fine product from the AirGunLab....

Bob
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 29, 2016, 04:18:07 PM
Congrats, Bob.  A job well done.  Very nice results.  I too can't wait till you can stretch it's legs out in the spring.

Joe
Title: Re: Regulated Disco Double
Post by: grumpy on December 30, 2016, 05:11:28 AM
Can't wait to see you stretch her legs out some  ;)
Title: Re: Regulated Disco Double
Post by: Dairyboy on December 30, 2016, 05:33:43 AM
Agreed can't imagine a 70fpe .22 that would sure be a fun gun
Title: Re: Regulated Disco Double
Post by: Monkeydad1969 on December 30, 2016, 06:29:55 PM
Man, can't wait to unleash my soon to be beast.  You curious now, guys?

Again, very nice Bob.

Joe
Title: Re: Regulated Disco Double
Post by: rsterne on January 04, 2017, 02:59:07 PM
I wanted to find out what affect the Velocity Adjusting Screw on the back of the receiver had, and document it, so I did some testing today.... I tried three different weights at each of the 10 settings (1 turn apart) on the 8-32 adjusting screw by shooting a few shots, taking the average velocity, and plotting the results.... Here is that data....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/DD%20Reg22%20Adjuster_zpsquvbpdqk.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/DD%20Reg22%20Adjuster_zpsquvbpdqk.jpg.html)

The nose of the bolt doesn't quite block the barrel port completely, because the front end of the port is rounded to streamline the flow into the barrel.... and when you first start obstructing the port, the velocity doesn't start to drop until you turn the screw in a couple of turns, even though you can see the nose of the bolt through the back of the barrel and transfer port.... I presume this is because there is a bit of wasted volume in the back corner of the chamber, causing a bit of pressure loss when the bolt is fully retracted, which counterbalances the obstruction of the hole when you first start moving the bolt forward.... The black line represents my best estimate of the percentage of barrel port available at each turn of the adjusting screw....

Note that at 2000 psi, the 18 gr. JSB Heavies are Supersonic, hitting nearly 1200 fps.... in fact they don't drop below Mach 1 until the port is about 50% obscured.... I was interested in finding a setting in the mid 900s with each weight, so that I could run a string with each pellet/bullet.... It turns out that with the 18 gr. JSB Heavies I only needed the adjuster open 2 turns, and with the BBTs 4 turns, compared to wide open for the 34 gr. JSB Beasts.... I then used those settings and shot a string starting at 3000 psi, until the velocity dropped off.... Those strings are shown below....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/DD%20Reg22%20Adjuster%20Strings_zpsqqbtdjat.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/DD%20Reg22%20Adjuster%20Strings_zpsqqbtdjat.jpg.html)

You will note that with the 34 gr. Beasts I get 10 shots, averaging 67 FPE, before the velocity starts to drop off.... With the 30 gr. BBTs, I get 11 at 57 FPE.... and with the  18 gr. JSB Heavies I get 15 shots at 36 FPE.... The efficiency is slightly lower with the BBTs, 1.13 FPE/CI compared to 1.18 with the Beasts.... and even lower with the 18 gr. heavies, down to 1.00 FPE/CI.... This is in sharp contrast to what happens to the efficiency if you back off on the hammer spring preload to reduce the power, instead of choking up the ports.... It makes perfect sense, because choking the port has little effect on how much air the valve releases (other than a bit of increased backpressure), because you aren't really changing the dwell, you are just forcing the air to flow through a smaller port, which is less efficient.... This means that for a quick adjustment in velocity to go with an ammunition change, the Velocity Adjusting Screw is great.... but if you are after increased shot count there are better methods.... Reducing the hammer strike will give you great efficiency, but the velocity will bump up below the setpoint.... A better way is to reduce the regulator setpoint AND the hammer strike, as I showed with the 18 gr. JSBs much earlier in this thread.... I have found previously, however, that a combination of all 3 methods produces the best shot strings with lighter pellets.... In my .25 cal Disco Double, with the basic tune set to shoot 50 gr. bullets at 100 FPE.... the best strings with JSB Kings were achieved with a lower setpoint, less hammer strike, and a slightly restricted barrel port.... It's nice to have the option of that added tuning element when you want to go plinking....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on January 04, 2017, 03:38:03 PM
The second half of today's testing was penetration and expansion testing of the different pellets and my new Bob's Boattails, both the 29.6 gr. FN and the 27.4 gr. HP.... I used the same settings of the velocity adjuster as for the strings above, 2T out for the 18 gr. JSB Heavies, 4T out for the BBTs, and 9T out (wide open) for the 34 gr JSB Beasts.... The test medium is my standard "Melt-and-Pour" soap, cast into blocks big enough to stop the bullet.... Here is a photo of the block with the four rounds inside it....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Penetration_zpsjkpwlfqh.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Penetration_zpsjkpwlfqh.jpg.html)

The BBT Hollowpoint is entering from the left (at 57 FPE).... From the right, top to bottom, are the 18 gr. JSB Heavy (at 36 FPE), the 34 gr. JSB Beast (at 67 FPE) and the 30 gr. BBT FN Solid (at 57 FPE).... Those FPE levels are the result of wanting all the bullets to be in the mid 900s fps range when they hit the block of soap.... The 34 gr. Beast had by far the greatest penetration, at 6.5".... The 30 gr. BBT and the 18 gr. Heavy were nearly identical, at 4.2" and 4.1" respectively.... while the 27 gr. BBT HP exploded violently and dumped its energy by creating a large cavity before stopping only 2.4" into the soap.... The volume of the wound channel in the block is roughly proportional to the FPE.... I then cut the block apart to photograph the wound cavities with the bullets still in place.... Here is the photo of the 18 gr. JSB and the 30 gr. BBT FN....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Expansion%2018%20gr%20Heavy%20and%2030%20gr%20BBT%20FN_zps0zvlbcap.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Expansion%2018%20gr%20Heavy%20and%2030%20gr%20BBT%20FN_zps0zvlbcap.jpg.html)

Now you can see why the BBT stopped in about the same distance as the 18 gr. JSB.... even though it had way more FPE.... The pellet hardly changed at all, which the large Meplat of the BBT expanded to well over bore-size, while leaving a much larger diameter wound channel than the pellet.... kind of the difference between an ice-pick and a sledge-hammer.... Next is the photo of the 34 gr. Beast and the BBT HP....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Expansion%2034%20gr%20Beast%20and%2027%20gr.%20BBT%20HP_zps6azzugdg.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Expansion%2034%20gr%20Beast%20and%2027%20gr.%20BBT%20HP_zps6azzugdg.jpg.html)

The block cracked behind the JSB Beast, so I didn't get to photograph it, but the wound channel was long and thin.... and you can see the pellet was hardly changed at all by the 67 FPE impact.... Not so the 27 gr. BBT Hollowpoint.... It literally blew apart after entering only about 3/4" into the soap, leaving three large fragments of the nose (and 1 small one) behind as the base (and 1 more fragment) continued penetrating.... Below is a photo of the bullets and pellets after recovery.... BBTs on the left, pellets on the right....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Bullets%20and%20Pellets_zps2eitkcji.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Bullets%20and%20Pellets_zps2eitkcji.jpg.html)

As you can see, round nosed JSB Pellets punch through and penetrate with very little change in shape.... Both pellets showed a very slight flattening in the center of the nose, and you can see how the skirts have obturated (blown out) from the pressure inside the skirt.... The Meplat on the BBT FN solid nearly doubled in diameter, showing how effective the large (70%) Meplat is in providing energy transfer to the target while limiting penetration.... The Hollowpoint BBT, however, is in another class entirely.... The nose section blew apart, creating a wound cavity in the soap nearly 3 calibers wide, while the rear portion of the bullet mushroomed completely and continued to penetrate, although less than 60% of the distance penetrated by the solid.... I would suspect that bullet to be devastating on Varmints.... and look forward to trying it out in the Spring....

Bob
Title: Re: Regulated Disco Double
Post by: rsterne on January 05, 2017, 05:17:15 PM
I made one additional test today, I reinstalled the SSG.... I had not tried it since I increased the hammer travel to 0.75" and adjusted the setpoint to 2000 psi.... There was no problem getting either weight of BBT into the mid 900s with a decent gap, and I could just barely push the 34 gr. Beasts at 950 fps (68 FPE) with the gap adjusted to zero (but no preload).... There is still room to increase the hammer travel slightly, which would give me room to create a gap and still shoot the Beasts at 70 FPE.... but with the stunning performance of the BBT Hollowpoints in my expansion tests, and assuming I can get them to shoot accurately, I think I will set the gun up for those.... With the gap increased to 0.10" (2.5 turns out), the velocity with the 27.4 gr. HPs was 960 fps, and I shot a 10 shots string with an ES of just 10 fps (1%) using just 740 psi of air.... and a LOT quieter.... That works out to 1.45 FPE/CI, a 28% increase in efficiency compared to the same spring with preload at the same FPE.... The gun is a bit harder to cock, which could be fixed easily by using a longer, softer spring, but I don't have one on hand at the moment.... It sure shows the benefit to an SSG over a conventional setup, though.... With the ability of this gun to be filled safely to 3500 psi, I should now be able to get two 10-shot mags on a single fill, which at 56 FPE is pretty impressive....

Bob
Title: Re: Regulated Disco Double
Post by: oldpro on January 06, 2017, 10:30:31 AM
 Bob I need to make a lot of money and hire you full time Your work is astounding!!!!!
Title: Re: Regulated Disco Double
Post by: rsterne on January 06, 2017, 05:42:09 PM
Thanks, Travis.... High praise indeed....  8)

Bob
Title: Re: Regulated Disco Double
Post by: Christopher on February 18, 2017, 03:56:42 AM
Bob,
What is your conclusion on the performance of your VBT that you incorporated on this build?

Thanks,
Chris
Title: Re: Regulated Disco Double
Post by: rsterne on February 18, 2017, 08:23:32 AM
I really like the resulting barrel rigidity of the large diameter CF shroud over a stub on the receiver.... and I like the ease and repeatability of the VBT system.... Accuracy testing will have to wait until the spring, as we still have 2 feet of snow on the ground right now....

Bob
Title: Re: Regulated Disco Double
Post by: Christopher on February 23, 2017, 03:00:11 AM
Hello Bob, got to re-reading about this build and came across something that I wanted to ask you about.

What is the hole at the rear and top side of the breech for? And also I'm assuming that you are fastening the barrel down with eight screws, two every 90 degrees on the barrel?

Couldn't figure out how to put your pictures in this post. I'm referencing Post #19 (hope that this link works) http://airgunguild.com/pcp-c02-and-helium-powered-airguns/regulated-disco-double/15/ (http://airgunguild.com/pcp-c02-and-helium-powered-airguns/regulated-disco-double/15/)

Thanks,
Chris
Title: Re: Regulated Disco Double
Post by: rsterne on February 23, 2017, 12:00:45 PM
The hole at the rear of the breech, just behind the cocking slot, is to hold the back of the breech down, as per a normal Disco / 22XX breech.... The screw head can pass through the large hole in the top, and sits in a counterbore in the bottom of the breech, with the threaded part through the smaller hole in the bottom, and it screws into the top of the rear SSG plug.... 

Yes, the barrel is retained by eight 10-32 setscrews (two rows at 90* intervals), into shallow cup recesses in the barrel....

HTHs....

Bob
Title: Re: Regulated Disco Double
Post by: Christopher on February 23, 2017, 02:57:57 PM
Quote
The hole at the rear of the breech, just behind the cocking slot, is to hold the back of the breech down, as per a normal Disco / 22XX breech....

Yeah, I had forgotten how my Disco breech was attached....been so long since I shot it and fiddled with it any.

Thanks again for the response to my questions,
Chris
Title: Re: Regulated Disco Double
Post by: Knife on March 08, 2017, 06:25:07 AM
Wow-Just WOW!!! Bob! :o

What a wonderful ride following along with this ultra in depth project. simply "Out Standing" :)

And I was so proud with the meager results I have so far been able to achieve with my little Maximus here in .22.


But then again, you gave me the specs for that project as well. 8)

A Hug Thank You Bob! ;)

Knife