Air Gun Home :: View topic - A New Method for Increasing the Efficiency of a PCP

lorraine · Member

Is that a remachined BNM breech or do you powder coat your projects before you start to carve out to what WE think is a masterpiece and hide the machine cuts on a mod BNM breech?

rsterne · Moderator

Nope, it's my own creation.... a prototype for a repeating breech that never came to production....

Bob

rsterne · Moderator

I was curious what I could get for efficiency using the SSG.... so I took my 2260 HPA, which is regulated at 1600 psi, and started dialing back the power and recording the pressure drop for 20 or 30 shots, using 18.1 gr. JSBs.... Here is what I came up with....

This is the first time I have had an efficiency greater than 2.0 FPE/CI.... At just under 12 FPE, I got 2.12 FPE/CI, which is 7.7 barcc/FPE.... That would give me 250 shots per fill on the 13 CI tank.... Adjusted for 23 FPE, the efficiency would be 1.7 FPE/CI and 100 shots per fill.... The way the gun is normally tuned, at 37 FPE, I can actually shoot down to 1400 psi without velocity drop, and I get 60 shots (6 mags.)....

Bob

rsterne · Moderator

For some time I have been wondering how effective the SSG would be on a CO2 gun like the Crosman 2260.... I had the opportunity to try that out today.... The testing started out with the gun configured exactly as a stock 2260.... Stock valve, hammer and spring, stock transfer and barrel ports, and a 24" barrel, although the gun did have a Crosman steel breech on it.... I loaded a brand new 12 gr. CO2 cartridge, fired the gun twice to pierce the cartridge, and then shot a string using 18.1 gr. JSB Heavy pellets until the velocity dropped to 300 fps, at which point I stopped.... I fired one shot every 30 seconds, and the temperature was 68*F.... I then repeated the testing using a much lightened hammer that was 50% of the weight of a stock one.... In both cases the stock rear cap was in place, so the preload on the 2260 spring was completely stock.... I then fitted an SSG, using the same spring, with as much preload I could use and still cock the gun with no gap between the end of the guide and the hammer.... I adjusted the gap to 0.020", installed a new cartridge, fired two shots to pierce it, and then fired another string.... The results are shown in the graph below....

There are some interesting things to note.... In stock form, even though I was only shooting every 30 seconds to limit cooling, the velocity declined in a near linear fashion for 30 shots, and then dropped rapidly, with a total of 37 shots above 300 fps.... I calculated the FPE of every shot and added them up, getting a total of 341 FPE from a 12 gr. cartridge.... With the lighter hammer, the initial velocity was lower, but within 15 shots it leveled off, staying within a very narrow ES for another 30 shots before dropping, with a total of 53 shots above 300 fps.... The total FPE from that cartridge was 457 FPE, which is pretty good, and a 34% improvement over stock.... With the light hammer and the SSG, the velocity stabilized quite quickly, and I got over 60 shots before it started to decline.... and the initial decline was not as dramatic.... and I got a total of 78 shots above 30 fps.... over twice as many as stock.... The total FPE from a cartridge with the SSG fitted was 627 FPE, breaking my own previous record of 608 FPE with an 18" barreled 1750.... That represents 84% more energy from a 12 gr. than I got stock....

I am extremely pleased with the huge increase in FPE per 12 gr. CO2 obtained by using the SSG.... This was, additionally, the first attempt using an SSG on a CO2 gun for me, and breaking the 600 FPE mark without tuning was pretty impressive.... I look forward to trying some different settings to see if I can get even more energy from a 12 gr. in the future.... but right off the bat, we know it works great on CO2....

Bob