When I was a skinny kid, 135 pounds, I borrowed a double twelve guage to hunt with--didn't own a shotgun of my own at that time. It was an old hammer gun. Decided to test-fire it. Loaded both barrels, and yes, cocked both hammers. Fired the right barrel, the damn thing doubled on me, the curved steel butt plate slammed into my bony shoulder, and I had a nice black-and-blue mark for days.