I was told to put clingfilm between resin and stock.

Worst problem I had ... well, nearly: an Airsporter I was asked to rescue as it would not cock .. lever would not move all the way. Turned out the piston/buffer was stuck. Ok, no real problem. But there were vice marks on the cylinder. Once I managed to remove piston and investigated further it turned out the vice had been tightened so tight, presumably by the person trying to get the piston out, that the cylinder had become a tad oval. Not much but enough to create a tight spot.
I dread to say that I did manage to get it better but it took time.
Cheers, Phil