41 arrested in ATF, Chicago police sting targeting machine-gun conversion devices
The 41 arrests and 64 machine-gun conversion devices seized were the culmination of a two-month operation. Police have linked the devices to mass shootings nationwide.
CHICAGO – An operation targeting trafficked illegal firearms and machine-gun conversion devices linked to "violent criminal activity" in Chicago and across the United States yielded over 40 arrests, federal and local authorities said.
As part of the initiative, the Bureau of Alcohol, Tobacco, Firearms and Explosives and the Chicago Police Department announced on Aug. 5 the arrests of 41 people, including a person who was previously convicted of threatening a mass shooting, the recovery of 171 firearms, and 64 machine-gun conversion devices. The two-month initiative was led by the ATF’s Crime Gun Intelligence Center of Chicago.
"This operation directly addresses the proliferation of machine-gun devices inflicting trauma in our communities," said Chicago Police Department Superintendent Larry Snelling. "Far too many lives have been lost to the senseless violence that only becomes more dangerous and fatal because of these conversion devices."
Court records show the operation consisted of a scheme where people sold conversion devices to undercover agents. Of the 41 cases, 18 are being prosecuted in federal court, the ATF said. The remaining 23 cases are being coordinated by Multi-Jurisdiction Bureau Chief Maureen McCurry of the Cook County State’s Attorney’s Office and Assistant Attorney General Greg Gansmann of the Office of the Illinois Attorney General.
'Recent proliferation of MCD's is a threat to our progress'
The operation comes at a point where law enforcement nationwide has struggled to get a handle on the spread of the conversion devices that can turn a regular handgun into a machine gun. The number of suspected conversion devices seized across the United States grew 784% between 2019 and 2023, according to the National Firearms Commerce and Trafficking Assessment.
In 2024, Chicago police seized 604 machine-gun conversion devices, up from 81 in 2020, authorities said.
"Combatting gun violence is my office’s highest priority, and there is no doubt the recent proliferation of MCD’s is a threat to our progress," said Cook County State’s Attorney Eileen O’Neill Burke. "A firearm equipped with one of these devices and an extended magazine can fire off 30 rounds in less than two seconds, terrorizing our neighborhoods and too often catching innocent bystanders in the crossfire."
National Integrated Ballistic Information Network showed that many of the recovered weapons are connected to violent crimes, including homicide and aggravated assault, that took place in the Chicago area and across the United States from 2017 through 2025, according to the news release.
How do the devices work?
The machine-gun conversion devices look like small, innocuous plastic components. But they can turn readily available semi-automatic handguns into machine guns, with extended magazines allowing them to fire even more rounds.
Alonzo Velasco, one of the 41 arrested, instructed undercover agents to install the conversion devices "behind the trigger," court records show. In place, a shooter only needs to pull the trigger once to fire off multiple rounds, according to court papers.
The devices can be made using the same 3D printers used to generate car parts and jewelry.
"This one-inch piece of plastic is killing people," Leigha Simonton, the U.S. attorney for the Northern District of Texas, said in announcing an operation to go after the devices. "Machine-gun conversion devices can turn Second Amendment-protected firearms into illegal weapons of war, and petty criminals into brutal killers. We cannot have our streets turned into war zones."
A standard 3D printer can make about 100 plastic switches in 72 hours, according to the ATF. Switch-equipped gun can fire shots faster than the standard M-4 machine gun issued to U.S. soldiers.