All Springer/NP/PCP Air Gun Discussion General > Engineering- Research & Development

Hammer Bounce

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Ok so I'm trying to build this 257 rifle. I copied the valve, hammer, springs, and travel length from my .308 build. The .308 works fine but in the 257 I'm getting hammer bounce. I have 2 springs that work in the .308, a 10# and a 15#. With the 10# spring the hammer will bounce once or twice. Hard to really count them it happens so fast. With the 15# spring it will bounce 3-4 times.

I'm kind of at a loss in what to try next. Change the hammer weight? Poppet size? Or something else?

Thanks Ricky

What is the basic rifle?.... For example, an Air Force based design is completely different than a conventional valve....


It's more of an Airforce design. Conventional valve but the transfer port is behind the breech. Basically the air makes a u turn and comes in behind the bullet. No bolt, just a chamber excess port.

OK, so the valve stem does not go into the breech, so there is no opening force on it like in an Air Force.... What else did you change when you swapped over the barrel from .308 to .257?.... Did you change any springs, preload, hammer, hammer travel, transfer port, anything else?.... Or, was the barrel the only thing that changed?.... What bullet weights were you using in .308 and what are you having trouble with in .257?.... Also, is the valve semi-balanced or conventional, and what is the throat and port sizes?....


bear air:


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