I build trebuchet. I have a small one that my kids use. It has a 2 foot throwing arm with 16 pounds of counterweight. It will throw tennis balls and golf balls about 80 feet with poor tuning, but it keeps them in the yard.
Last October I drove to Oklahoma to help a friend assemble and run his for a local event. We took first place in the intermediate category with a 1503 foot throw using a 9 pound pumpkin. Including the weight of the hanger it has 2,000 pounds of counter weight and the long side of the throwing arm is about 12 feet.
This video shows the one I built for the kids in hinged counterweight configuration (kids mode) and whipper configuration (big kids mode). The whipper setup doubles the distance with this machine but misfires get much more violent and common due to details.
This is the same machine in kids mode with my daughter. She was 4 at the time. The trigger is 100% automatic, just push the arm down and it sets.
These two are the big one I helped assemble and run. First is from behind with me running the camera.
This was the same shot. If you watch, the arm and the counter weight both hit the trigger on their way by.