HaveBlue didn’t print an entire gun, he printed a “receiver” for an AR-15 (better known as the military’s M16) at a cost of about $30 worth of materials.

The receiver is, in effect, the framework of a gun and holds the barrel and all of the other parts in place. It’s also the part of the gun that is technically, according to US law, the actual gun and carries the serial number.

When the weapon was assembled with the printed receiver HaveBlue reported he fired 200 rounds and it operated perfectly.

via The End of Gun Control? - Forbes.