IIRC, the Cardew's said it's around 1400-1500 psi, but it could spike quite a bit higher than that if combustion (note, not dieseling) is taking place.... which according to them is common in springers shooting over about 600 fps....Bob

IIRC, the Cardew's said it's around 1400-1500 psi, but it could spike quite a bit higher than that if combustion---is taking place....which according to them is common in springers shooting over about 600 fps....

...I would say we need a lot more than 1500psi at the pressure peak.

If we ignore dieseling (unless all guns diesel a significant amount):A piston gun might give 5fpe per cubic inch (swept volume) of air.We adiabatically compress one cubic inch of air. We get 5fpe during the adiabatic expansion. The peak pressure should be a fairly simple formula. Anyone want to take a crack at it?I would say we need a lot more than 1500psi at the pressure peak.

Quote from: Scotchmo on March 23, 2012, 01:42:16 AMIf we ignore dieseling (unless all guns diesel a significant amount):A piston gun might give 5fpe per cubic inch (swept volume) of air.We adiabatically compress one cubic inch of air. We get 5fpe during the adiabatic expansion. The peak pressure should be a fairly simple formula. Anyone want to take a crack at it?I would say we need a lot more than 1500psi at the pressure peak.A Hatsan 125 has a swept volume of 79.5 cc and generates 1000 fps in .22 caliber . . .1000 / 79.5 = 12.578616 fps per ccDave

Quote from: Tarheel on March 24, 2012, 06:21:14 PMQuote from: Scotchmo on March 23, 2012, 01:42:16 AMIf we ignore dieseling (unless all guns diesel a significant amount):A piston gun might give 5fpe per cubic inch (swept volume) of air.We adiabatically compress one cubic inch of air. We get 5fpe during the adiabatic expansion. The peak pressure should be a fairly simple formula. Anyone want to take a crack at it?I would say we need a lot more than 1500psi at the pressure peak.A Hatsan 125 has a swept volume of 79.5 cc and generates 1000 fps in .22 caliber . . .1000 / 79.5 = 12.578616 fps per ccDaveThat needs more boundary conditions; my generator has 25 cubic inches per cylinder and if you hook a 22 parrel to its spark plug I guarantee it won't spit out the pellet at anything near 1000 fps. We need compression ratio, and time to do the compressing. If it is too slow we just modify the compression ratio by slowly shoving the round down the barrel. Soooo...figure the two extremes, one the pellet does not move before the piston is at the end of its travel, and the other where it gets half way down the barrel. What are the peak pressures then? What we'll actually see will ov course be somewhere in the middle...and we do need to worry about gamma changing across this compression. Even a 6:1 change in volume is enough for the variation of gamma to effect the calculation...cheers,Douglas

... be somewhere in the middle...and we do need to worry about gamma changing across this compression. Even a 6:1 change in volume is enough for the variation of gamma to effect the calculation...cheers,Douglas

How is your calculus/integration? I can't solve it but I did do a rough numerical integration of the isothermal model and I got over 3000psi. I suspect that the adiabatic model will be closer to 1000psi.