Machine-gun fire has appeared on ShotSpotter detectors thousands of times across the U.S., marking a dramatic increase over the past three years, CNN reports. Experts blame the widespread availability of inexpensive "auto switches" or "auto sears" that convert semi-automatic weapons to fully automatic. "Not since Prohibition have we seen this many machine guns being used to commit crimes," said Tom Chittum, who spent more than two decades with the Bureau of Alcohol, Tobacco, Firearms and Explosives, and retired as its No. 2 official before signing on as an executive with ShotSpotter earlier this year. Gun laws virtually eliminated automatic weapons from city streets for decades, Chittum said. "But now machine guns are back, and they're everywhere."
Data from ShotSpotter, the private company that cities pay to install sensors that detect gunfire, showed roughly 5,600 machine-gun incidents last year among the 130 cities with ShotSpotter. In 2019, there were about 400 incidents. There has been a corresponding spike in seizures of conversion devices by ATF in recent years, from fewer than 100 in 2017 to more than 1,500 last year. A CNN review of court filings in cities across the U.S. found dozens of cases in recent years involving so-called conversion devices or semi-automatic handguns already converted to fully automatic. The increasing availability of auto switches has been driven in part by the ease with which they can be made using cheap, 3D-printed parts and instructions available online, according to Earl Griffith, the chief of ATF's Firearms and Ammunition Technology Division.