14 DAY TRIAL // The state of Philadelphia is no longer the only part of the world where creating and owning 3D printed plastic guns is illegal. As of December 9, 2013, undetectable firearms (plastic ones as it were, 3D printed ones included) are under strict regulation.
Back in the 1980, the Undetectable Firearms Act was established, in order to prevent plastic weapons from passing through metal detectors and used in important and crowded places, like airports, banks, embassies, etc.
The act was going to expire this year, but on December 9, it was decided by the government that it would be extended. So, in the US at least, plastic guns continue to be tightly regulated.
3D printed guns are, of course, at the middle of this, because the law's potential expiration coincided with the release of the 3D printed Liberator pistol by Defense Distributed. From now on, you'll need special permits to 3D print weaponry.
Curiously though, the Undetectable Firearms Act doesn't mention 3D printing at all. The Liberator and its ilk do fall under it though. It's not a perfect measure by any means, but it should appease most people.