The Science Channel has a series of awesome videos (you won't believe the centrifugal catapults in action) that can give you an idea. Consider: currently, the record for the Air Rifle class is 4483.51 feet, and 2737.69 feet, for the Centrifugal class. That's chunkin', folks.
ONAGER ONLINE is a cheerfully enthusiastic site of one of the international competitors, Onager, who came in second place in the European championships. Love the team logo in the foreground: nails the spirit of the endeavour.