Lazs, if you've ever been in any type of speed shooting competition, its similar but more restrictive.
You can only use single action revolvers, lever action rifles shooting pistol caliber rounds, and shotguns designed before 1897 (which includes double barrel "coach" guns, either with or without external hammers), or pump action shotguns with an exposed hammer like the Winchester 1897 (most famous as a WWI trench gun). You can also use lever action shotguns.
It is a blast. Pardon the pun.

Its not just black powder though, they use all sorts of modern rounds. Black powder (Pyrodex) is just my choice. Last competition I had to borrow guns to compete and the guy who loaned me his guns had the SWEETEST matched set of .38 Rugers. Consecutive serial numbers even. The trigger pull had been modified to be very light and with that heavy a frame the .38 had almost no kick at all. Superbly easy to stay on target. Rifle shot the same rounds, except he used flat nose bullets instead of standard rounds. 20 ga. double barrel with double hammers and 18in. barrels. I couldnt miss with that setup. Ok I missed one. Got greedy and went for too much speed on the last round.
Here's one pic of me at the line, second pic is me and the guy I borrowed the guns off of.
