Williams designed and built four semi-automatic rifles while in prison. All four used the high-pressure gas within the breech as a cartridge was fired to operate their semi-automatic actions. The means used to accomplish this was a floating chamber containing the cartridge that channeled the gas at the front of the chamber to force the floating chamber backwards into the bolt with sufficient energy to operate the action. Rearward movement of the chamber was limited to a short stroke to impact the bolt face, in effect making the floating chamber a short-stroke gas piston. All four rifles are part of the permanent David Marshall Williams display in the North Carolina Museum of History.