He is going to soil himself when he finds out those can be used to make magazines, stocks, and other parts. You can even make a shoulder thing that goes up.
Defense Distributed (Google for it) has a 3D printer file to make an AR lower. They're also developing two pistols, one that's to be a "teaching weapon" to aid development of a fully mechanical version. No shoulder thing that goes up is mentioned on their web site, but hope springs eternal.