Situation: shooter had double feed on his Turkish semi-automatic shotgun Phenoma. Bolt somehow moved forward and hitted the primer while he was trying to take one of the rounds out of a shotgun which led to a accidental discharge outside of a chamber:
This happened to one of the shooters on shotgun competition. Firing pin on his Benelli Supernova stuck in forward position and slamfire discharge occured when he pushed forend forward loading shell into a chamber.
The problem was in firing pin. It is little deformed (probably from dry-fire trainings). That caused it to stuck in forward position. It looks like the metal is too soft and easy to deform: