I agree w/ 2-piper. The softer primer usually causes the problem described.
Firing pin protrusion,,I've always set them betw .035 & .045.
No chisel points to the tip. Nice semi circle polished tip.
It isn't that the primer necessarily needs an overly deep indentation to fire, but it does need sufficient energy in what strike it does take.
Anything deeper than necessary into a primer cup just buries the tip in there.
Even rebounding firing pins can get stuck in primers and make opening the action near impossible.
Couple that with what may also be a problem in the gun,,that being the cocking linkage having some loosness in it's take up as the bbl starts to drop open.
The hammer w/the firing pin down hard onto the fired primer isn't retracting as the bbls make their initial opening movement.
So the firing pin(s) drag across the primer as you initially open the bbls.
Depending on the wear or fit up of the linkage, some can be especially bad.
Add a soft primer cup and/or an overly long pin, it can end up being one of those over the knee opening specials when both bbls are fired.
