Sen. Ed Markey’s (D-Mass.) little-known 3D Printed Gun Safety Act (S. 2319) would criminalize sharing firearm schematics for 3D printers online. 3D printing describes a process that allows people to “print” 3D models for various items. These models range from small tools, art projects, and shapes up to functional firearms. Critics of the practice have called these 3D-printed firearms “ghost guns” because they lack serial numbers and are difficult for law enforcement to trace. Despite their relative novelty, 3D-printed firearms have a rich legal history. In 2018, Congress passed the Export Control Reform Act (ECRA), a foreign policy bill designed to restrict enemies’ access to U.S.-made munitions. In March 2020, 22 states argued that 3D firearm schematics violated ECRA because they were accessible to foreign enemies. They brought suit against Defense Distributed (D.D.), a firm that provided schematics for 3D firearms. The plaintiffs argued that these schematics would cause them …