A friend of mine purchased a derringer in .45 ACP. It only has 1.5" barrels (double barrel, stacked). One day he turned one of his old 55 gallon drums over and was going to shoot holes in the bottom to turn it into a trash burning barrel. He stood back about 5' from the barrel and shot once. The bullet dented the bottom of the barrel and bounced back at him, striking him in the leg. It wasn't moving fast enough to even bruise his leg. I've never even considered carrying a derringer as a self-defense gun, and that just convinced me I was right.
