I would examine closely the bottom edge of both firing pins when
they are fired and protruding from the breech face.If this area
is not nicely rounded and smooth it can cut into and bind with the side of the primer indentation and make the initial opening of the gun difficult.You can correct this by cello taping the face of the breech to avoid marking,with the pins protruding,and then either
filing or stoning the bottom edge of the pins.This has worked for me several times. Terry

Better to keep your mouth shut and be thought stupid,than open it and confirm.