3 targets against the berm, maybe 3 yards apart. Depending on your skill level, start at 10, 15, 25 etc. yards. At the sound of the beep you'll fire one round into the first, 2 into the second, 3 into the third, 4 into the second again and 5 into the first, for a total of 15 rounds. Obviously only good hits count. Add one second to the time for any round outside of the 8" circle. This is a great drill to keep you thinking while you shoot. It gets shooters out of the regimented "BANG BANG" next target "BANG BANG." When the S hits the fan, the bad guy may not go down after only two rounds. It may require 4 rounds or more to stop the threat. It also practices multiple targets, as well as speed vs accuracy.
Simple, but effective.