I can see quoting an FPE value per CI of swept volume.... but what is the point of using fps unless you specify the pellet weight?.... it's apples and oranges....Is there a particular reason people don't want to use Cardew's numbers?.... just curious....Bob
Quote from: rsterne on March 24, 2012, 11:18:27 PMI can see quoting an FPE value per CI of swept volume.... but what is the point of using fps unless you specify the pellet weight?.... it's apples and oranges....Is there a particular reason people don't want to use Cardew's numbers?.... just curious....Bob12.578616 fps per ccAt 5fpe/ci, that Hatsan 125 should shoot 11-12gr pellets at 1000fps. That is reasonable but actual FPE would be better than leaving us guessing at the pellet weight. It looks like 5fpe is reasonable for both small chamber volume guns like mine or large volume guns like the Hatsan.For my use, the peak pressure is less important than the math/model that can predict it. The same model should be able to predict the pressure at any point along the barrel. And from there, the optimum barrel length for a given system. For my current gun, I did a progressive chop until it started to lose power with most types of pellets. By then, I was two inches too short. So I replaced the barrel with one that was two inches longer (though it was 7 inches shorter than stock).
The swept volume of the Hatsan is 79.5 cc which is 79.5/16.4 = 4.85 CI.... 29.1 FPE / 4.85 CI = 6 FPE/CI.... A bit higher than the 5 FPE/CI that Shotchmo was suggesting as an example to use, but in the ballpark.... One pet peave, if I may.... When one number in a calculation has only 3 significant figures (ie 958), the answer should also have only 3 significant figures.... ie 29.1 FPE.... The extra decimals cannot be justified.... OK, I'm anal and I admit it.... Bob
OK, I'm anal and I admit it.... Bob
The swept volume of the Hatsan is 79.5 cc which is 79.5/16.4 = 4.85 CI.... 29.1 FPE / 4.85 CI = 6 FPE/CI.... A bit higher than the 5 FPE/CI that Shotchmo was suggesting as an example to use, but in the ballpark....
Indeed! Were it NOT for combustion then we would all be shooting springers that perform like 10 meter guns.
its producing around 163 psi per shot in the chamber
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
...K-sqrd is saying a spring gun uses 3,318 psi to get 17 fpe ...
... If you think its going to read 3,318 psi you are out of your mind...
... you think you can produce 3,318 psi with a single stroke of a spring ?...
Something for you guys to play with and some info. The pic is interactive, click on the dots.http://www.arld1.com/images/swfs/pistonpelletdynamics.swf