Windham Weaponry's 450 Thumper semi-automatic utilizes a gas impingement system. The flattop upper receiver is forged 7075 T6 aircraft aluminum with an aluminum trigger guard, carpenter 158 steel bolt, and manual lever safety. The receiver is with laser engraved the caliber and has safety indicator markings on both sides. The 450 Thumper has a 16 chrome-lined barrel made of 4150 Chrome Moly Vanadium 11595E steel with an A2 flash suppressor. It has a Luth-AR buttstock with an adjustable buttplate and cheekrest, WW free-float forend, and Hogue over-molded beavertail pistol grip. It includes a (5) round magazine, black web sling, and hard plastic gun case.