E-mail me the link to 3D printout plans for a fully automatic weapon when you have it.Unless by then the UN has taken over the internet so it can stop the spread of weapons , the likely real consequence to this evolution.
You don’t need 3D printing to build a lower receiver, just a metal working shop. The Afghans build AK-47s in very primitive conditions. And you don’t need printing to make a fully-automatic weapon, just a little work on the lower receiver of a semi-automatic weapon (NB the Afghan AK-47s again).
Fully automatic weapons that are hand held are way over rated . What a clever fella would want is a S.A.R.T (Surgical A$$hole Removal Tool)such as the Welrod pistol or the Deslisle Commando Carbine. These are weapons that are integrally suppressed & fire from a closed/locked breach so they are extremely quiet.
They are also far easier to make as they are even simpler mechanisms/sub-assemblies.