Homemade machine guns: 3D-printed ‘switches’ can land you in prison

MARTINSBURG, W.Va. – In the basement research lab of the agency that regulates America’s firearms, two dozen 3D printers hummed, stringing thermoplastic filament into computer-designed patterns that would harden and eventually become a gun.
At the Bureau of Alcohol, Tobacco, Firearms and Explosives National Services Center, a sprawling complex behind high steel fence in the hills of West Virginia, ATF staff download the latest blueprints for guns and for the add-on devices called “auto-sears.” These small pieces modify guns for rapid-fire and are classified as machine guns themselves.
As the $2,500 printers showed, hobbyists and criminals can easily exploit rapidly improving technology. The agency is trying to keep up.
On Friday, ATF Director Steven Dettelbach and Deputy Attorney General Lisa Monaco announced new initiatives to crack down on the proliferation of 3D-printed “machinegun conversion devices,” MCDs, that may resemble a bottle opener or Lego, but convert semi-automatic rifles and handguns into guns capable of illegal automatic fire.
At ATF’s research facility, firearms enforcement officers are just as fluent in calibers and rates of fire as “slicing” or the process of converting a digital model into printing instructions for a 3D printer.
In 39 minutes, for 40 cents in materials, they had printed a piece of plastic that could sell on the street for hundreds of dollars. It could also land you in prison for 10 years.
“MCDs can transform a street corner into a combat zone, devastating entire communities,” Monaco said. “The proliferation of these MCD devices requires our immediate and sustained attention.”
Monaco announced a new Department of Justice committee to develop strategies on the devices; a training protocol for law enforcement to spot and seize the devices; and a U.S. attorney-led effort to prioritize cases involving the devices.
U.S. attorneys in individual states have previously attempted enforcement actions with buzzy names like Operation Flip the Switch, Operation Kill Switch and Project Switch Off in reference to the nicknames for the Glock “switches” or “chips” that attach to the popular handgun to turn it into a machine gun.
In addition to the enhanced focus on finding and charging producers of the illegal devices, the ATF is looking for help from both academics and the 3D printing companies, known as the additive manufacturing industry.
ATF’s Dettelbach said the industry could do more to stem the illegal misuse of their products.
“We can’t fix this threat to public safety alone. We need to raise awareness, educate the public and we need to enlist outside help with collaboration from the best minds to make real progress,” Dettelbach said.
Dettelbach said the devices now represent the majority of illegal guns seized in firearm trafficking cases nationwide.
After years of raising alarms, gun safety groups applauded the effort Friday to find new solutions for the machine gun conversion devices.
Nick Suplina, senior vice president for law and policy at Everytown for Gun safety, equated the effort to those by color printers decades ago to help prevent counterfeit currency. In that case, businesses stepped up to put controls into place to prevent scanners and printers from helping criminals.
“This is an extremely serious problem that will only get worse as the tech gets better, so it is essential that the private sector work with law enforcement on gun safety solutions,” Suplina said. “In the era of 3D printing, we must do the same for downloadable guns and accessories.”
Personally made firearms that fire one shot at a time are legal, as is 3D printing certain guns as a hobbyist. But further manufacturing faces a key legal test in October when the Supreme Court will hear arguments in a case about “ghost guns” without serial numbers and parts kits.
Some cities, like Chicago, have turned the focus toward Glock itself in lawsuits despite the company having no association with the illegal devices that counterfeit its trademarks. Chicago and other states argue the handgun giant should make its weapons more difficult to convert.
The latest ATF accounting of the devices suggests thousands of the imported or home-printed pieces of plastic are already in circulation in the United States.
In a tour of ATF’s testing facility in West Virginia, agency officials said manufacturers often market the illegal devices online with code words such as “keychains,” “bottle openers” or “fidget spinners,” when in reality they’re solely designed to modify rifles or pistols into machine guns.
The 1934 law that banned Thompson submachine guns includes language banning the devices since they fall under the definition: “Any part designed and intended solely and exclusively or combination of parts designed and intended for use in converting a weapon into a machinegun.”
Officials have pointed to the 2023 shooting death of Brackenridge Police Chief Justin McIntire in Pennsylvania as evidence of the deadly consequences of the devices. The man who shot McIntire used a pistol equipped with an extended magazine and illegal conversion device.
They’ve also been used in mass shootings, such as the 2022 shooting in Sacramento that left six dead and 12 wounded; and a 2019 shooting by a street gang in Fresno, California, that killed four and wounded six.
Nick Penzenstadler is a reporter on the USA TODAY investigations team. Contact him at [email protected] or @npenzenstadler, or on Signal at (720) 507-5273.