Maybe you can search for my old trebuchet thread. I built 14 of them. As #3 seemed to have the very best geometry, I scaled it up and down. I made 6 tabletop versions for tossing olives and ice cubes (50') at banquets. Counterweights were the lead balls for fishing down-riggers. Sold them all for $50 each. Anything planned for more than 300lbs in the counterweight is essentially stationary. Castle wall busters were never mobile armament, especially on soft British soil after 6 weeks of rain!