We made this trebuchet in the basement, without plans. The counterweights are two commercial fishing 25-pound lead weights covered in two thick layers of "Performix Plasti Dip" plus the chains, and the pumpkins were between 1 and 1 1/2 pounds. The baseball went the farthest, at 40 yards / 120 feet, and weighs the standard 5+ ounces. The sling is made of 4 layers of your average tough grommeted plastic-like groundcloth available everywhere, covered with two layers of duct tape, then new grommets added. The first shot with the baseball was very low, so we adjusted the angle of the release hook once after that and left it alone for the rest of the shots. The ratios and lengths of the long and short arms and the sling string were determined from this excellent mathematical analysis of the trebuchet: http://www.thehurl.org/tiki-download_file.php?fileId=9 (less info)