GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on October 02, 2012, 09:44:06 PM
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I've finished up my 2260 HPA with the reversed tank.... The final touch was a DAQ walnut stock for a QB that I altered to fit the 2260 trigger group and shortened to miss the tank.... It is finished with 6 coats of Watco Danish Oil, sanded progressively to end with 600 grit, and then a coat of Minwax.... It turned out to have a beautiful tigerstripe in the grain on the cheekpiece, an unexpected bonus.... I added a Pachmayr buttpad for protection and to lengthen the pull slightly.... The scope is a Leapers 3-9 x 32 AO MilDot.... The gun weighs 7 lbs. 2 oz. all up....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/2260HPA.jpg)
I fitted a prototype breech I designed that uses a 10-shot MRod clip.... It is designed to accept a full length 3/4" OD shroud.... I have a similar breech on my Grouse Gun that uses an 8-shot PRod clip.... The tank block I machined from aluminum, and it has a 3-slot Picatinny rail on the bottom for a BiPod or other accessories, and incorporates a barrel band on the top.... The Power adjuster screw is hollow, and the hammer is fitted with a spring guide that protrudes when the gun is cocked.... That guide serves three purposes, it adds mass to the hammer, keeps the spring straight, and acts as a cocking indicator.... The gun shoots as good as it looks.... I`m getting 45 shots at 36 FPE from 1700 psi on the 13 CI tank, which works out to 1.06 FPE/CI....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/2260HPAReversedShotString.jpg)
I finally received my 3000 psi gauges (200 psi increments) from China, and fitted one to the 13 CI tank in place of the stock 6K gauge.... Compared to the larger gauge (100 psi increments) on my tank yoke (which reads the same as the one on my pump), this mini gauge reads exactly the same from 1000 psi to 2500, and then a bit of error creeps in, it reads a bit high at a 3000 psi fill.... That doesn`t really matter, as I fill using the gauge on my tank.... The regulator setpoint is 1600 psi, and I can shoot down to 1300, although four 10-shot clips leaves me at 1500 so that`s a good place to refill as the velocity hasn`t started to drop off yet....
This isn't so much a new build as a rebuild of the rifle I used to collect about 100 ground squirrels this past spring, so I already know how it shoots.... All I can say is.... lookout next year.... ;D
Bob
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Fantastic work there. Your projects never cease to amaze me.
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Very Nice work
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Another piece of art and great craftmanship. I love reading the writeups on HPA projects posted by you and Ribbonstone. While I am not an engineer by any stretch of the imagination they inspire my tinkering.
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great job!
how did you get it to shoot so flat?
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The gun is regulated at 1600 psi with a 65 cc plenum, and the hammer spring is set so that if it was unregulated the velocity would peak at about 1500.... That means the gun is always shooting right near the top of what would be it's unregulated sweet spot, whether the reg is slightly above setpoint (due to creep when the tank is full when the pressure may be ~1650 psi) or below setpoint (down to about 1300 psi there is no meaningful change in velocity).... Setting it up that way also helps the efficiency (ie shot count and noise level)....
Bob
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sweet!
im using a ninja tank on the build im working on now.i put the belleville washers in as directed.the valve is stock. i hope my gun shoots as flat as yours
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nice work ;) are you using a disco valve or a 2260 valve, what about the tube?
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45 shoots at 36FPE wow sir wow
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great work, I'm working on a QB 78 according to your posts, I'll keep you posted how it develops.
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I'm using a Disco valve with an extended, big bore front end, and no gauge block.... Valve mods are not quite as drastic as yours, I don't like the idea of a 3/16" transfer port in a .22.... I'm using a stock diameter (0.166") poly port, with the valve and barrel ported to suit.... I am building a .25 cal version, and it has a 1/4" valve throat and 3/16" ports.... It is currently over 50 FPE at 1800 psi, I'm hoping to bring that down to 1600 psi if possible.... It has an 18 CI tank to feed the bigger bore....
Bob
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I'm using a Disco valve with an extended, big bore front end, and no gauge block.... Valve mods are not quite as drastic as yours, I don't like the idea of a 3/16" transfer port in a .22.... I'm using a stock diameter (0.166") poly port, with the valve and barrel ported to suit.... I am building a .25 cal version, and it has a 1/4" valve throat and 3/16" ports.... It is currently over 50 FPE at 1800 psi, I'm hoping to bring that down to 1600 psi if possible.... It has an 18 CI tank to feed the bigger bore....
Bob
by big bore front end do you mean the cap that you designed to seal the tube before the roll stamp? Yeah I didn't feel comfortable with going 3/16" and almost regretted it but its not bad at all actually, I did spend A LOT of time deburring and polishing the barrel port, I can load any pellet and it actually loads a lot better than before I did any mods to the rifle. I don't have to hold the rifle at an angle or anything, just hold the rifle level and slip the pellet in the breach and push the bolt forward, it all feels buttery smooth(something I did not expect at all). Did you start a thread on your .25 build?
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Absolutely amazing Bob! Great job! 45 high power shots is just awesome (and without a regulator!). I bet it will look even better with the shroud.
Harry
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Absolutely amazing Bob! Great job! 45 high power shots is just awesome (and without a regulator!). I bet it will look even better with the shroud.
Harry
huh? the gun is regulated, did I miss something?
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Sorry, Harry, the gun IS regulated at 1600 psi.... You can see the regulator at the front of the tank, screwed into the tank block....
Bob
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Very nice Bob. I always enjoy seeing what you come up with. Is that a 250cc bottle?
I am also interested in the .25cal project you mentioned. 50+fpe at 1800 is impressive. I don't know how heavy the projectile is that you are shooting, but I'd bet it is heavy. I based a very basic model from the info you presented. I figured that with a 43gr projectile, 1725psi would be the min psi. Obviously barrel length as well as other factors would have influence. Basically I used the porting dimensions to find the possible flow at a given psi. 1725psi, with the porting you have, will deliver .760ci . That is enough to get 725ish fps from a 43gr pellet/bullet. 50fpe.
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The tank on the .22 cal is 13CI (213 cc).... The 52+ FPE on 1800 psi was with JSB Kings.... I got 55+ FPE at 2000 psi and 48+ FPE at 1600 psi.... With EunJin 43 gr. I got 67+ FPE at 2000 psi (didn't try them at lower pressures).... The barrel is 24", 1/4" throat, 0.115" stem, 0.188" transfer and barrel ports....
Bob
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Bob, at 2000psi, using 43gr and a 24" barrel, looks like .842ci is what is available. I'm seeing 840fps, using .800ci of air at 2000psi, for 67.3fpe. At 1600psi, looks like .856ci is max possible flow. All other conditions the same, I say 740fps range for 52+fpe, using .850ci .