Addendum:
I had a friend who's late Grandfather had a fire before breech locked incident with a model 12 in the 1940s. The gun had a broken firing pin, which made contact with the primer before the breech was locked. The gun is an early model 12 in 12 gauge, friend still owns it, and you can clearly see pellet marks in the receiver and chamber area of said gun. Grandpa fixed the gun himself, and it works well to this day. Grandpa's hunting companion that day didn't hear very well out of the ear closest to the gun for a few days after.
Even if a gun design will "slam fire" I suspect it isn't a good idea to make a regular practice of it.
Best,
Ted
