hi bruce check the size of the transfer port, if it was a origanal leather seal rifle one been converted to a synthetic seal you might have to alter the port size, you might also have a leaky transfer port end [renown on older 35`s] and it letting all the air out of the babbly brazed joint so not cushining the end piston stroke and slamming into the comp tube end, you could do with doing a leak test on the comp tube
atb john