A gunsmith has created what is believed to be the first gun made partially by using a 3D printer. He has made a .22 caliber pistol by printing a ar-15 lower receiver, and mating it to an off the shelf upper reciever.
Apparently he has been working on making a full blown .223 AR-15 with the same lower receiver without sucess, though he seems to blame the commercial upper receiver rather then the printed lower receiver.
Worth noting it cost him $30 to produce the lower receiver, and with the more modern 3D printers he estimates cost would be ~$10. A fraction of the normal price for an off the shelf lower (~$200 +/-)
And of course with the lower receiver being plastic, it makes one of the most easily recognizable parts of a gun easier to bypass security screenings.
Interesting stuff. Though it certainly raises a host of moral and legal issues.
Brief article- with links, here