The so-called firing pin is integral with the hammer on Fox guns, it's the tip of the hammer. If the right hammer tip was sticking out because it wasn't cocked that could cause a premature fire when the gun was closed. Check to be sure the hammer retracts fully when opening the gun. Decock the gun and then open very slowly while listening to the clicks when each hammer is cocked. If the right hammer cocks at the very end of the opening motion it's possible it was never cocked or just barely cocked when you opened the gun with a partial opening movement. The other possibility as others have noted is a worn sear tip/hammer knotch that jarred off when the gun was closed. Personally I would verify/deny the hammer cocking scenario before I suspected the worn knotches. I hope this helps. Silvers
