....he made an AR-15 lower receiver, not an "assault rifle". Yes, technically that is the only part of the weapon classified as a firearm, but calling it "printing a gun" is kind of dumb. For reference, here's what a lower looks like:
Interesting, but lots more expensive to purchase the equipment than to just buy an $80 receiver... not to mention you'll still need an upper receiver, barrel, BCG, FCG, stock, buffer, grip, etc etc.