I can’t remember the name of the case. Years ago the Supreme Court ruled that a firearm was not easily convertible to a machine gun if it required the use of a machine shop.
As far as I know no one has made a gun with a 3-D printer that isn’t destroyed with the first shot. But we are hammered constantly with proposed laws and regulations regarding printed firearms. This is the problem: Our public servants, elected or appointed, spend their time on fantasy matters, rather than doing the work we hired them to do.
How about a lot of time and a couple good files. Does the machine shop have to have a lathe and a mill or just a mill. How about a harbor freight mill? I believe someone could easily convert a AR to full auto with out a mill or lathe. John Browning once converted a lever action rifle into a full auto. Couple of operating rod along barrel connected to a funnel in front of muzzle on one end and lever on other. Funnel allowed bullet to pass, but muzzle blast pushed funnel forward, operating lever, springs sucked back rods closing lever and a toggle on lever tripped trigger and bang bang bang.
A 3D printer guns still got a ways to go. But the printers are fun.
A blocks of good steel, aluminum or brass, a drill, files and some stuff from the hardware store and a bunch of time and I believe I could make a open breach full auto similar to a M3 grease gun. Way easier with my mill and lathe. Why would it even need a rifled barrel to spew a bunch of rounds at short range.
Only thing that has stopped me is it would be a felony.