I came across this drill in a Pat McNamara book titled, T.A.P.S. The shooter starts out ten yards from an IPSC target. The shooter will choose their own standards based on their skill level. Standards include what the par-time will be. The shooter will use a shot timer and on the beep, fire continuously as many shots as they can until the par-time beep sounds. This signals the shooter to cease fire. The shooter will choose their punishment for themselves for each shot placed outside of the A zone. Penalties can include things such as running a lap for each shot placed outside of the A zone or 25 push-ups for each shot placed outside the A zone, etc.
This drill will give the shooter an idea of how quick their split times are, while at the same time not compromising accuracy for speed. This will also break the habit of drawing and firing a set number of rounds.