Algodoo

Alright. First entry was disqualified for size. This should be alright I hope. It is no bigger than the sample trebuchet. So far in my tests, it hit the same spot 10 out of 10 times which got to count for something Just press play

EDIT: Measured accuracy again. Its accurate down to about ½ meter over 400 meters, which I suspect is better than most medieval versions

EDIT 2: Updated the scene with a ruler and lowered the counterweight with 10 kgs. Should hopefully be alright now.