For those not familiar with what 3D printing is, it is a lot what it sounds like. A digital copy of an object is created, and it is printed out on a printer that prints in 3 dimensions, and instead of using ink to print, the medium is usually a plastic.
These people basically downloaded the digital copy of an AR-15 lower receiver made of plastic, mounted on an AR-57 upper which fires 5.7x28mm and tested it to destruction 6 shots later.
This is the website i found the story.
I can definitely already see the lawmakers and politicians practicing speeches in mirrors to make this sort of thing as illegal as murder.
I'm sure its going to stir up a lot of opinions. Personally i think they should have figured out how to make this work with .22LR because it probably would have gone longer than 6 shots.