I shoot Gamebore's black powder shells in my Remington 12g 1894 AE. The barrels are thick and heavy, so I feel pretty good when pullin' the triggers. I'd have to say, the gun doesn't get much of a workout - it was bought just to have an American damascus gun around.
I think the barrels are the thing, no matter how careful your loads are. Pitted barrels might cut loose with a bottle rocket fired from 'em!