Tuning M3 tuning glitch

[easyridemm]

I am posting this for a good friend of mine. He has been a big Impact fan for years. He has become a master at tuning these guns. He has owned and tuned every model of Impact up to and including the new M3. Needless to say he knows what he is doing when he tunes an Impact. He tunes his guns to be as accurate as possible using as little air and hammer spring tension as possible to achieve the desired speed and accuracy. He just purchased a new M3 in 25 cal. We spent 6 hours trying to tune this gun. We tried every possible combination of Reg. Pressure both 1st and 2nd stages, both hammer spring adjustments, and the fine tuning valve out front. The gun will shoot 4 shots with a spread of no more than 3 FPS. The 5th shot will be 30 to 50 FPS. faster or slower. It will repeat this at any combination of settings. Has anyone ran across this in their M3? Any ideas will be appreciated very much. 

 

[nervoustrig]

Common causes of an occasional velocity drop or jump:

1. Hammer inconsistency. Could be friction caused by a burr or roughness, galling, or binding of some kind.
2. Sear drag (not likely in a gun with a drop sear trigger group).
3. Bolt or breech O-ring beginning to fail. Seals on some shots, not on others.

Less common causes:

4. Vacuum formed by the hammer flying forward, especially if a wet lubricant is being used.
5. Subtly bent valve stem.

May want to also inspect the valve limiter internals to make sure it's assembled correctly and that the bumper isn't damaged. 

 

[biohazardman]

Another not so likely but possible problem might be the magazine not allowing the pellets to be seated properly or damaging them in some way. Five or six shots without the magazine could quickly rule this out.

 

[Pistonjohn]

Another not so likely but possible problem might be the magazine not allowing the pellets to be seated properly or damaging them in some way. Five or six shots without the magazine could quickly rule this out.

This. Try single shot to eliminate this possibility.