finger squeeze and a magazine to feed a stream of bullets. the result is one could logically only use in a war. or, like las vegas, a massacre. >> be advised it is automatic fire. fully automatic fire from an elevated position. >> reporter: you would think that kind of weapon power would be illegal for average gun owners to possess. think again. this is a slide stock. perfectly legal, aftermarket component. according to the manufacturer's video is, it's easy to assemble on an assault rifle and the ruts, though technically do not make a machine gun, ask yourself if you can tell the difference. >> that was just one of several ways that you can make a semiautomatic rifle into a fully automatic rifle. >> reporter: the slide stock is legal to buy and to use. former atf agent sam rabati