The technicalities presented go a little further. Because the frame isn't considered a component of the weapon by itself, DD insists that you build the frame and insert the steel before printing anything else, as indicated above. That way, it's impossible for you to build an illegal weapon.

Building a gun is something of a philosophical exercise. At some point, like the Ship of Theseus, you have a collection of parts; at some point you have a firearm. Legally, it's generally more specific — and since most philosophical questions don't carry the risk of jail time if you answer wrong, nearly everyone I spoke with erred on the side of interpreting the law conservatively. Since the Liberator uses custom parts, it's primarily the detectability issue that DD is concerned about. Follow its instructions, and in DD's estimation the weapon is itself legal.

The next question was whether or not it was legal for me to have it in my possession. David Kennedy, the director of the Center for Crime Prevention and Control at New York's John Jay College, was pretty clear that it wasn't.

New York City has a variety of permits that might apply in this case. The first that Kennedy cited was the "premises permit." With such a permit, I would be allowed to have a handgun in my home, transport it to a firing range while secured and unloaded, and use it at the firing range. When I was done, same process in reverse.

I was very much not allowed to carry it in public. For that, I would need a carry permit. For that, I'd need to demonstrate "specific need" — like being a security guard. Those, he said, were rarely granted. And "without the possession of one of those two permits," Kennedy told me, "you are not permitted to carry a handgun in New York City." I indeed had neither.

The third question ended up being the biggest one. Could a business or other third party legally print the pieces for me?

Setting aside the issue of the steel slug, no expert I spoke with felt that the printing establishments bore much risk. I spoke with James Jacobs, professor of Constitutional Law and the Courts at New York University. "If the law says it is unlawful to make the gun or part of the gun without a license," he said, you can't do it. Otherwise, "you can do what is not proscribed."

The Bureau of Alcohol, Tobacco, Firearms and Explosives has a FAQ on gun manufacture. Barring machine guns and some shotguns:

Firearms may be lawfully made by persons who do not hold a manufacturer’s license under the GCA provided they are not for sale or distribution and the maker is not prohibited from receiving or possessing firearms.

Sounds good. But there's a bit of philosophy tucked in there. What is "for sale" in this case? Does hiring someone to print a piece of a gun count as selling a gun part? The printers I spoke with weren't generally interested in testing that line. That is, once I found some printers.