Hammer Bounce

[sixshootertexan]

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

[rsterne]

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

Bob

[sixshootertexan]

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.

[rsterne]

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?....

Bob

[bear air]

Following.

[sixshootertexan]

Ok this is 2 different guns. The .308 is a conventional bolt gun. You've seen it before. The .257 is a new gun. Conventional lower with boltless upper.
I'm using the same component design.

The .308
https://i.postimg.cc/t4tPThnB/DSC00325-zpsvxtfpyny.jpg

The .257
https://i.postimg.cc/pL9bHdRy/257-4.jpg
https://i.postimg.cc/CxtbknHw/20221014-185121.jpg

[sixshootertexan]

[rsterne]

OK, so the valves, both springs, and hammer weight and travel are all identical?.... What about the porting from valve to breech?.... It looks like the .308 bolt does not retract, so there must be a probe in the chamber?.... Do both valves have springs, and are they the same?....

Bob

[sixshootertexan]

Yes all identical.  Porting is .25" in both. The .308 has a retractable bolt.

[JPSAXNC]

Less hammer travel might help reduce the bounce.

[rsterne]

Bullet weights in both calibers (I am interested in any difference in SD)?.... Pressures?....

Bob

[sixshootertexan]

NOE Molds
.308 135 BBT
.308 155 BBT
.257 100 BBT

[sixshootertexan]

Do you think an SSG will help?

[rsterne]

Providing you can get enough hammer strike to open the valve, most definitely an SSG should get rid of the hammer bounce.... I would try for 3-5 lbs. of preload and about 1/16"-1/8" of gap between the valve stem and hammer face when uncocked, that is ideal.... You can get away with more gap, but over 1/4" and you may see slight difference in velocity shooting uphill or downhill.... It's a matter of balancing spring rate, preload, and gap....

Bob

[sixshootertexan]

Ok so 4 1/2 lbs compressed my spring .270". I preloaded the spring .200" and I have .160" of free travel on the hammer. I'll get the rifle together and test as soon as I can.

[sixshootertexan]

Ok I got to test the SSG today. It worked. I'm ecstatic. Now I can proceed with the project. I only test fired it twice. I didn't have time for more testing today. I got some other things done that I need to do. I grabbed the rifle and put 2 rounds through it for testing while at the range.