Ah yes, the terrifying “ghost gun.” The latest boogeyman trotted out whenever politicians need another excuse to chip away at the Second Amendment. Whether anyone likes it or not, technology has changed the game. Today, people with modest mechanical skills can use 3D printers and CNC machines to manufacture modern firearms in their own workshops. In many cases, they can produce a Glock-pattern pistol that is virtually indistinguishable from one that rolled out of the Glock factory. That genie is not going back into the bottle. Laws attempting to regulate every privately manufactured firearms or  sound suppressor are little more than political theater. They may sound impressive during a press conference, but they are virtually impossible to enforce against millions of hobbyists, machinists, engineers, and basement workshops spread across America. Then comes the familiar refrain from government officials: “We can’t trace guns without serial numbers!” Really? In the overwhelming...