The firing pin really has nothing to hang up on and i would bet that your extractor/ejector is causing the problem. The extractor/ejector is tripped when the gun is being opened to remove spent shells and it is possible that you have a burr or another gremlin in that portion of the gun causing you to be unable to open the action. Numrich gunparts has schematics that can aid you to trouble shoot the problem. That's where I'd start. Hope this helps.