Print Your Own AR-15 Receiver at Home, Annoy Cory Doctorow and the Brady Bunch

Back at Penn State one of my friends has had an interesting idea percolating in his head for a while. The machine shop on campus has some rapid prototyping machines where you feed it a 3D model of something in a computer file and it will happily “print” that object for you, turning a virtual rendering into a real world (and metal) object. My friend’s idea was to model a 1911 receiver using the software, print it, and then smuggle it off campus before the local cops got wind of a student using University machines to make guns. My friend eventually gave up on the idea (and now writes for TheFirearmBlog, actually), but it turns out someone else took the master plan to the next step. And then released the files online.

The widespread availability of cheap 3D printers has led to a boom in websites where people post models of things they’ve designed. Everything from intricate clocks to that one part that always breaks in Ikea furniture is available as a download, just grab the file and shove some plastic into your little printer and VOILA! Instant replacement part, often better than the original.

Something where this technology hasn’t really taken off is replacement parts for firearms. Currently, the methods available to those at home use plastic or metal with a relatively low melting point and build the object by layering the material and slowly building up the shape. The same characteristics that make the materials excellent for use in 3D printers (malleability and low melting point) make them not so good for holding up to the effects of recoil and the heat a firearm produces. Well, maybe something in .22lr, but definitely not a 5.56mm NATO rifle. And definitely not anything that’s not already made out of plastic.

Firearms parts are one thing, but what about the receivers themselves? With receivers, there are two very important considerations: one of the technical kind, and another of the legal kind.

If you were to fabricate your own AR-15 lower, there’s a very good chance that it will literally blow up in your face. Even though the recoil from a 5.56mm NATO cartridge is most decidedly on the “gentle” side of the spectrum that doesn’t mean that it’s light enough for plastic to handle. Smith & Wesson started making .22lr ONLY AR-15 clones not too long ago with plastic lowers, and one of the major concerns raised by those in the know was that if they were ever used for anything larger they might fail catastrophically and injure the shooter.

The reason for the safety concern isn’t specifically from the heat or the direct pressures around the chamber (even those would probably eventually kill the lower as well). The major concern is from the single greatest point of stress on the part: the threads that attach it to the buffer tube. Every time the gun goes off, those threads need to not only withstand the forces of the buffer going back and forth, but also the shooter’s shoulder pressing on the stock. After a few rounds the threads will most likely start stripping off, which could lead to a failure to seat malfunction or even a premature detonation blowing up the entire receiver assembly.

Not good. Very not good. Definitely wouldn’t want to be the EMT on duty for that one.

The other consideration we must, um, consider… is a legal one. Despite what Cory at BoingBoing may insinuate, it is perfectly legal for an American citizen who is legally allowed to purchase a firearm to make a firearm themselves. Some states may have regulations in place (like NY and CA’s assault weapons ban) that prohibit you from kitting out the rifle however you want, but as long as you stay within the letter of State and Local laws you’re fine. One of my friends just put the finishing touches on an MP5 he welded together, and I must say it looks (and shoots) fantastic.

You don’t even really need a serial number unless you want to make it into an SBR (like my friend) or plan to sell it, but it’s probably still a good idea. You can choose whatever serial number you want, so my friend chose ###0001 for this build. Leaving room for a few thousand more, I suspect.

The same general rule applies if you print your firearm instead of welding. The only issue you may run into is if you use one of those companies where you send them a design and they mail you a completed part — at that point THEY manufactured it and shipped it, making them illegal gun dealers. Technically.

Another legal serial number consideration is that according to the ATF, the serial number MUST be engraved in metal. A different crazy friend of mine used to work for Cavalry Arms, who made plastic AR-15 receivers with BUILT IN buttstocks, eliminating the issue with the threads stripping out of the stocks completely. They stamped their receivers the same way Glock stamps their frames — on an embedded strip of metal.

What’s the moral of this story? The best thing to take away from this development is to think before you act. Sure you could print your own AR-15 lower, but would it be useful? How about legal, especially if you live in Great Britain or Australia?

On the other hand, how great would it be to show up to a Brady Campaign rally with a 3D printer and just start churning these things out?

Click here for the design for the AR-15 Lower.

Click here for the design for the AR-15 Magazine.

Be safe, be smart.

[h/t: Martin]