Interesting milestone in open-source 3D printing over at Thingiverse: User crank has published a freely-downloadable magazine for the ubiquitous AR-15 rifle. As downloaded, crank’s magazine only holds five rounds, but a person with basic 3D modelling skills could modify it with little difficulty to produce a “high-capacity” magazine. I’m not sure what the current state of law on magazine size limits is, but prior to the sunset of the Federal Assault Weapons Ban (Wikipedia) in 2004, manufacture of an AR-15 magazine with a capacity of more than 10 rounds was an offense.
Crank reports that the magazine—which consists of a printable body, follower, spring, and baseplate—is fully functional, at least for a few rounds:
I have used this magazine, no jams or feed problems….. YET. It works, but be reminded it is only a printed ABS magazine. If you end up using a printed ABS mag spring be prepared for stress relaxation of the polymer over time, especailly [sic] if it is kept loaded over a long period of time.
As published and as printed by crank himself, I should emphasize, this magazine is (as I understand it) completely legal, and would’ve been legal even before the ban expired. But the file raises some interesting questions.
In response, user KingLudd has uploaded a printable lower receiver for an AR-15. If you own an AR-15 rifle and want to buy replacement parts for it, you can easily buy—in person or through the mail—every part of the gun except the lower receiver, without any kind of legal controls on, or records of, the sale. So the manufacture of a lower receiver is tantamount to the manufacture of a functioning, extralegal, unregistered AR-15.
Unlike crank, KingLudd has posted no photographs of the printed part or otherwise done anything to suggest that he has actually printed and/or tested it, because actually doing so—absent a federal license to manufacture a working AR-15—is unambiguously illegal.
Update: The stricken sentence is false. At the federal level, at least, licenses are required only to manufacture AR-15 lower receivers for sale. Thanks to our commenters for catching and correcting the error, which was based on my mistaken belief that an AR-15 is a Title II firearm and hence subject to the provisions of the National Firearms Act. Apologies for the misinformation.