M34 problem

[LAalex]

Took the M34 out for a little target shooting yesterday and after about ten shots the shot cycle started to feel a little different-a little better actually-shorter and quicker.  Accuracy, however, was another matter.  It was all over the place.  I broke out the Chrony and sure enough I'd lost around 80 fps.-down in the 640's with CPHP's.  Whadday'all think?  Spring, seal?

Thanks,
Scotty

[Mark 611]

spring! or seals' either will cause this problem but a piston or breech seal will do the same 

[DMikeM]

Spring. My M34 broke it's spring after the second tin of pellets. Put in a JM kit and hated it. Now it has a Vortek kit and it is much nicer to shoot.