3D "printing" machines are just about at the point where they can "print" any
firearm reliably. There are videos of a working automatic assault weapon that was
assembled entirely from parts made by a machine that was given the dimension
data for each part. This is scary because a person doesn't need to risk owning
an illegal weapon. They can "print" the parts out that are defined in a computer file,
and then assemble it in minutes when they want to use it ... and then throw it
away to hide any evidence.