from http://www.kurzweilai.net/
A post in an AR15 fun forum describes the development, printing and testing of the 3D printing of the lower receiver of an automatic weapon. Although the barrel would be a much more difficult fete, the lower receiver is a crucial piece of the weapon (one of the CTLT staff was a rifle expert in the US Marines and knows this stuff). It is basically the hub of the rifle “wheel” in which the other components including trigger group, ammunition feed subsystem, upper receiver (with the barrel, bolt, etc.), and other optional components are connected. Therefore, the fearful pieces of a recent TED talk are made real in which the speaker introduced the idea that killers will not need to transport weapons any longer in the future because they could be printed once the killer is near the target.