Communities around the U.S. have seen shootings carried out with weapons converted to fully automatic in recent years, fueled by a staggering increase in small pieces of metal or plastic made with a 3D printer or ordered online. Laws against machine guns date back to the bloody violence of Prohibition-era gangsters. But the proliferation of devices known by nicknames such as Glock switches, auto sears and chips has allowed people to transform legal semi-automatic weapons into even more dangerous guns, helping fuel gun violence, police and federal authorities said.

The (ATF) reported a 570% increase in the number of conversion devices collected by police departments between 2017 and 2021, the most recent data available.

The devices that can convert legal semi-automatic weapons can be made on a 3D printer in about 35 minutes or ordered from overseas online for less than $30. They’re also quick to install.

“It takes two or three seconds to put in some of these devices into a firearm to make that firearm into a machine gun instantly,” Dettelbach said.