Could be the piston seal is too tight a fit, or you were sent the wrong spring or piston seal, or the breach seal needs replacing (get new ones in some of the kits), or chrono no good....the list goes on. Best thing to do is to contact Steve Pope firstname.lastname@example.org
, had the same trouble myself with a TX and I tried loads of things before contacting Steve
. Had to send my internals to him and result was the kit was OK. Turned out to be the cocking arm was worn where it attaches so it wasn't sealing at the breach.