If you must ever fire a Derringer...

Do not,
I say DO NOT!,
do as I did and loosen your grip on the little bastard!

I was firing a friend's over/under .410 Derringer. One trigger for both barrels. Let up on the trigger slightly to set the second shell and then squeeze for the second shell...except that it wouldn't!

I put the pistol at high port arms and requested assistance (the friend was a qualified range master). He checked the weapon over and had me let out on the trigger again (although I had heard the tell tale "click" that should have meant the trigger was set). As I was bringing the weapon back down to aim I found out what the term "hair trigger" meant. The second barrel fired and because it only has about 2.5 inches of well polished wood for a grip, and I had loosened my grip, it flew up and out of my hand! It didn't quite clear my head as it flew and the thumb grip on the hammer left a neat little gouge just about dead center on my forehead. I probably did more damage to my forehead than I did to the target with that second shell!