These guys made one in the past that broke after a few rounds, but seems they finally managed to come up with a design that is capable of firing a reasonable amount of rounds with out breaking.
3D printed AR15 lower receiver..
It's still a long way from just printing a gun on a 3d printer because this still depends on all the other regularly manufactured parts. It's just the lower receiver is the part that has the serial numbers, and that's the part that is usually registered.
I'm not up on the law with that kinda stuff, so I'm not sure what kind of legal issues it would bring upon someone whom downloaded it and reproduced it. Perhaps some GFY gun expert can tell us.
Same guys made working 30 round clips as well, pictured above.