That's a COOL contest.
We used to have a tire rim filled with concrete with a steel pole standing out of the axle hole. Attached to this a rotating collar with horizontal arms and on the end of each arm, was an 8" paddle. Running straight back from the swivel was another arm with a hook on the end. A bungee cord is attached to the hook and down to the pole.
2 Contestants stand off, side by side, guns pointed down, held in both hands. On the signal, they aim and fire at the 8" plate facing them. Range 50 yards for this duel. The first to hit the plate, spins it, taking his oppontents disk out of line of fire. It is a spectator sport as well and not difficult to see who hit and who didn't, even though the shots might be very close together.
A quick pointing rifle is the best for this. Hooked butt plates? well, they're fun to shoot against.