There's a few more links inside the following stories. Pretty amazing stuff.
HaveBlue reportedly used a Stratasys 3D printer to craft the part, assembled it as a .22 pistol and fired more than 200 rounds with it.
The tester then attempted to assemble a rifle with the part and a .223 upper receiver but had “feed and extraction issues.” The problem may not in fact be with the 3D-printed part, though, as the issues remained when a standard aluminum lower was used.
3D printed AR -15