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Air Gun Home Forum Index » Rifles » .25 cal Disco Pumper Carbine Goto page 1, 2  Next    View previous topic :: View next topic  .25 cal Disco Pumper Carbine   Posted: Fri Oct 12, 2012 6:38 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC I started work on the internal parts for my .25 cal Disco Pumper today.... It will use the MRod barrel and Disco breech I mated up the other day, plus an extended Disco valve with a check valve built in just ahead of the gauge port.... The valve extension will include a gauge mount for a 1500 psi gauge.... Here is the piston and the front mounting block to fit a Benjamin 392 linkage into the Disco.... There will be a barrel band mounted on the stub of the front block which projects 3/8" ahead of the shortened Disco tube.... The barrel band will be 1/8" behind the muzzle of the MRod barrel.... The next step is to cut the Disco tube to length, and machine an 8" slot in the bottom for the linkage.... and drill the hole for the front pivot pin.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Fri Oct 12, 2012 6:50 pm robert w Senior Member Joined: 12 Feb 2012 Posts: 574 Location: usa i want to see more .lookin good so far _________________ ,crosman 400,gamo big cat in .22, diana 5g,diana 54 air king, diana 34 in .22 diana 34 in .177, wilrauch hw-55,and a romainian pioner training rifle , and a huge collection of powder burners 35 last count . 1 would think i have a gun store   Posted: Sat Oct 13, 2012 5:55 am Big Ern Veteran Member Joined: 31 Aug 2011 Posts: 357 Location: Miami Fl. Wow! I can't wait to see this Bob. It will be epic!   Posted: Tue Oct 16, 2012 6:40 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC I machined the Disco tube today.... cut it to length and squared the end and then machined the slot for the pump linkage.... The tube is 1/2" behind the front of the MRod barrel, and the 3/8" barrel band will fit over the stub of the aluminum front plug.... leaving the front of the barrel band 1/8" behind the muzzle.... The pivot pin is 5/8" behind the front of the tube, and the slot is 8.2" long.... The stroke is 7.6" and the piston is 6.7" from the link pin to the compression face.... That leaves the compression face 0.3" ahead of the front of the gauge hole, which leaves room for the O-ring to seal the valve.... The next step will be to make the extended front end for the valve incorporating the gauge mount and check valve.... Incidently, the front of the Disco stock comes to just behind where the spring sticks through the lever (the bump in the photo).... It will be cut just in front of the gauge, with the forestock becoming the pump handle.... Should work perfectly.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Wed Oct 17, 2012 3:52 am Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND Interesting project! How many pumps do you expect to need for a full power shot Bob? Al _________________   Posted: Wed Oct 17, 2012 10:35 am rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Well, Al, I originally hoped for ~30 FPE on 10 pumps, but was told that won't happen, it will take 14-15.... All I can say at this point is "que sera sera".... what will be, will be.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Wed Oct 17, 2012 11:04 am Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND 14 pumps! I should take your De-Fib with you when you go shooting. Al _________________   Posted: Wed Oct 17, 2012 2:07 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC I do.... it's permanently installed now!.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Wed Oct 17, 2012 9:43 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC I got the valve front end done today.... Here are the parts.... The extended front end incorporates a shortened check valve from a male Foster fitting.... It is held closed by a 1" long 0.020" wire spring sitting against a washer located on a shoulder inside the valve front.... I opened up the last coil of the spring to 5/16" so that it can't get past the washer.... Behind the washer is a QB hammer spring, and the location of the shoulder for the washer was chosen to provide the same force holding the valve poppet closed as on a stock Disco valve.... This was achieved by drilling progressively deeper, assembling the valve, and pushing the stem against the stem of a stock valve until they opened at the same time.... The rear (spring) chamber of the valve front is drilled to 3/8" and the front portion to 5/16".... and then a 1/8" NPT hole intersects the front part for a gauge mount.... For initial tests, I will be using a simple male to female 1/8" NPT extension to mount the 1500 psi gauge, which is located in the stock position for a Disco.... At the moment the rear portion of the valve is dead stock....The total volume as built, including the gauge mount, is ~5.5 cc.... That gives me a bore/valve volume ratio of 3:1 with the MRod barrel.... I plan on boring out the rear portion of the valve to unshroud the poppet and increase the volume by nearly 1 cc.... and to drill the throat to 1/4", thin the stem, and increase the port diameter and angle it for improved flow.... but I think I'll try it with the stock valve initially.... Then comes the fun part.... I have made a gauge mount that connects a 16 gr. thread CO2 cartridge to the valve.... It has an internal volume of just over 20cc, and is rated at 250 bar MSWP, >500 bar burst.... It installs into the mount with 3/8"-24 threads which will be either glued or soldered to seal them.... The cartridge just clears the main tube, and will live in a hollow in the stock just in front of the gauge.... It will be invisible when the pump arm is closed.... With the cartridge installed, the total valve volume will be ~27cc, and the gun would, of course, be tuned to retain air and operate like a PCP with an onboard pump to top up the pressure between shots.... I'm pretty excited to see all the parts coming together for this project.... It won't be too long before I can install the parts in the tube and try out the pump.... I still have other parts to make before the gun can be fired, however.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Thu Oct 18, 2012 12:44 pm Mark5043 Silver Status Member Joined: 12 Apr 2009 Posts: 1379 Very nice Bob!...Now that is a pumper.. _________________   Posted: Thu Oct 18, 2012 7:44 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC I assembled the pump today, using a stock Disco rear valve half.... and a conventional gauge mount.... Valve volume is ~ 5.5 cc and the swept volume is ~ 54 cc.... The following pressures were achieved: 5 pumps - 600 psi 10 pumps - 1100 psi 15 pumps - 1500 psi After sitting for an hour, the pressure is still 1450 psi, which I would imagine is the effect of cooling.... I can't comment on the pumping effort as I had no stock on the gun, and it's not exactly easy to pump sitting upside down across my knees and pushing on the 1/4" wide metal pump linkage.... I would say the effort is significant but do-able.... and ergonomically shouldn't be a problem once the stock is fitted.... I'm quite pleased with these results.... I have to make the barrel band and the transfer port and a bolt, so initial testing isn't too far away.... I'm not expecting too much with the stock valve and porting, but need those results as a baseline.... I also have to modify the stock before any serious testing can be done.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Fri Oct 19, 2012 3:37 am Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND This certainly looks a goer, a PCP with built in pump independent of any ancillary backup. Depending upon the shot count It would be interesting to know what it would be in .177. Al _________________   Posted: Fri Oct 19, 2012 8:52 am WestTexasFarmBoy Member Joined: 27 Oct 2011 Posts: 17 Location: 33*40'17"N, 101*32'6"W That is quite a feat of engineering Bob. Even if it does take 15 or 20 pumps -- it will still be amazing _________________ FarmBoy's First Axiom of Forum Posting: "The only stupid question is one that should have been asked but was not even though the answer was unknown to the person who did not ask the question."   Posted: Fri Oct 19, 2012 11:29 am rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC With the extra 21 cc reservoir, it will be more like 70-75 pumps to fill to 1500 psi.... That is why the "Mk. 2" version will have a male Foster fitting.... I view the pump as an on-board top-up system for that gun.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Fri Oct 19, 2012 1:40 pm robert w Senior Member Joined: 12 Feb 2012 Posts: 574 Location: usa im amazed and enjoyin watchin a gun grow _________________ ,crosman 400,gamo big cat in .22, diana 5g,diana 54 air king, diana 34 in .22 diana 34 in .177, wilrauch hw-55,and a romainian pioner training rifle , and a huge collection of powder burners 35 last count . 1 would think i have a gun store .25 cal Disco Pumper Carbine     Air Gun Home Forum Index » Rifles You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum All times are GMT - 5 Hours   Page 1 of 2   Goto page 1, 2  Next All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First  Select a forum Main Forums----------------AirGunHome Q&AGeneral Air Gun Questions and TopicsPicture GalleryTarget Shooting: Casual, Fun and CompetitionHunting, Pest Control, Varminting People/Events/Airgun Issue Discussion----------------Introduce YourselfThe BS TopicClubs/Events/Regional/Political Airgun Issues Maintenance, Modification and Reviews----------------RiflesPistolsAntique, Collector and Novelty AirgunsBB GunsPellets/AmmoOpticsAccessoriesAirgun Smithing Buy, Sell or Trade Forums----------------For SaleWant to Buy   Note: If you are seeing "Please enter your username and password to log in." 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