Ghost guns?
They’re currently a favorite bete noire of the gun grabbers. Biden’s gonna soil himself with glee.
The ATF requires that a serial number be stamped on the receiver of all manufactured, complete guns. However, if you buy an "80%" receiver, one that has not been completely finished, mill out the area the trigger mechanism fits in, drill a couple of holes for the trigger pin, and then assemble the lower to an upper, which has the barrel and bolt carrier group, you have an Armalite-15. You buy all the parts separately, and presto, you have a functional rifle.
It is a "ghost" since there is no paper trail, the kind that the ATF is supposed to destroy after 3 months, that is being kept for 5 years and counting, since the ATF has been having "trouble" entering all the information from their copy of the 4473 for their data base.
AR style and select Glocks are the most popular, since the reivers are made out of aluminum, but you can also build a Colt M1911, among others.
Guns are not magic. You can build one with a moderately equipped machine shop and a little basic knowledge.
However, doesn't "ghost gun" sound creepy?