Five years ago, 25-year-old radical libertarian Cody Wilson stood on a remote central Texas gun range and pulled the trigger on the world’s first fully 3-D-printed gun. When, to his relief, his plastic invention fired a .380-caliber bullet into a berm of dirt without jamming or exploding in his hands, he drove back to Austin and uploaded the blueprints for the pistol to his website, Defcad.com. He'd launched the site months earlier along with an anarchist video manifesto, declaring that gun control would never be the same in an era when anyone can download and print their own firearm with a...