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DALLAS (NewsNation) — Law enforcement across the country is working to stop a disturbing, rising trend where criminals are using small, illegal devices to alter the ability of a handgun, turning it into a fully automatic weapon.

The small devices, about the size of a nickel, are called Machinegun Conversion Devices (MCDs) or “switches,” and they fit right into the 9 mm Glock handgun to allow the weapon to fire off an entire magazine in just seconds.

They are gun accessories that convert semiautomatic pistols to fire automatically, according to the Bureau of Alcohol, Tobacco and Firearms.

Under the National Firearms Act, MCDs are defined as machine guns even when not installed, NewsNation affiliate WXIN reported.

The device is illegal under federal law, with convictions carrying a sentence of up to 10 years in prison, NewsNation affiliate WOOD reported.

According to ATF, the number of guns with switches seized has increased more than five times from about 300 in 2020 to 1,500 in 2021.

“Switches” are becoming more popular for a few reasons: People can buy them online from China and Russia and they can be made on 3D printers.

In the Dallas-Fort Worth area, law enforcement seized 775 Glock switches last year, according to Dallas Police Department Chief Eddie Garcia. About 650 of those were seized over the course of one investigation in Fort Worth, where one alleged dealer was printing them himself, U.S. Attorney for the Northern District of Texas Chad E. Meacham said in a press release on the suspect’s arrest.

In another case last month, the U.S. Attorney for the Northern District of Texas Leigha Simonton announced the arrest of a dealer in Dallas who was accused of selling the conversion devices on Instagram.

Law enforcement agencies are working to shut down those websites, putting dealers behind bars to stop the flow of these devices on the street.

A former ATF agent demonstrated just how powerful and dangerous this alteration can be.

“These weapons are very hard to control, they fire so quickly that it’s literally spraying bullets unless you are very well trained in a machine gun,” Former ATF agent Scott Sweetow said. “So often innocent people get hit. It’s not just a gang drive-by shooting and hitting their one target, which is bad enough, it’s hitting innocent people, and that is exactly what is happening in shooting incidents across America.”

NewsNation reached out to Glock for comment, even though the company has nothing to do with the manufacturing of the devices, asking if it can do anything to change the model or frame of the guns so “switches” cannot be attached. The company did not immediately respond.

NewsNation’s Devan Markham contributed to this report.