My experience with this style of lock is ZERO but it sounds like a bit of upward preload is needed on the frizzen spring.Another thing I would do would be to make the pivot screw so the smooth shank of the screw would be deep into the bolster and no thrust from firing the lock could be transferred to the threads.A stub length would work for this.This lock may have this incorporated and it's easy to add if it does not.
I call it a very simple lock and that's good.
Bob Roller