FREEDOM: I Made an Untraceable AR-15 ‘Ghost Gun’ in My Office—And It Was Easy. “I did this mostly alone. I have virtually no technical understanding of firearms and a Cro-Magnon man’s mastery of power tools. Still, I made a fully metal, functional, and accurate AR-15. To be specific, I made the rifle’s lower receiver; that’s the body of the gun, the only part that US law defines and regulates as a ‘firearm.’ All I needed for my entirely legal DIY gunsmithing project was about six hours, a 12-year-old’s understanding of computer software, an $80 chunk of aluminum, and a nearly featureless black 1-cubic-foot desktop milling machine called the Ghost Gunner.”