The Mongolian Boys Society was out for revenge. Six members of the Fresno, California, criminal gang huddled in a vacation rental in November 2019, cleaning their guns in preparation to retaliate against the Asian Crips for the suspected killing of one of their own. 

According to court records, one of the “triggermen” carried a Glock pistol outfitted with an auto sear, a small device the size of a thimble that transformed his semiautomatic weapon into a machine gun capable of firing 20 rounds per second. Around 8 p.m., the crew drove across town to a palm tree-lined street. Moments later, in one of the backyards, they opened fire on a gathering of people. Bullets sprayed through the crowd, killing four and wounding six. 

But the house was not a rival gang den; police later determined that a family had gathered there to watch football together. Six members of the Mongolian Boys Society were arrested for their alleged involvement in the mass shooting. Three face the death penalty. 

An auto sear — the most common automatic conversion device — transforms a semiautomatic gun into a weapon capable of emptying an entire magazine with a single pull of the trigger. Also known as switches or chips, auto sears have been around since the ‘70s but are exceedingly tough to acquire legally in the United States, where machine guns cannot legally be owned without a special license. In recent years, these small metal or plastic devices have exploded in popularity on the black market and gained a particular cachet among criminals and anti-government extremists. Last year, members of the Boogaloo Boys, an accelerationist movement that hopes to spark a second civil war, used weapons equipped with auto sears to attack a federal courthouse. 

An investigation by The Trace and VICE News found that federal prosecutions involving automatic conversion devices have spiked in recent years. From 2017 to 2021, the number of cases jumped from 10 to 83, according to our exclusive nationwide analysis of court filings. We found over 260 cases filed in the last five years, including robberies, assaults, and murders, with over 1,000 devices recovered. The government has not previously compiled this data, and the actual number of illegally converted machine guns on the streets is likely far higher.

Olga Pierce

The Bureau of Alcohol, Tobacco, Firearms and Explosives, the federal agency responsible for policing guns in the U.S., said it seized 1,500 weapons modified with auto sears in 2021, a staggering increase over 2020, when only 300 were recovered. 

“Auto sears are everywhere on the street right now,” said Jefferey Boshek, a 21-year ATF veteran who now serves as the special agent in charge of the Dallas Field Division. “They’re one of the scariest things we’ve dealt with since I became an agent.”

The ascent of the auto sear has been propelled by its availability and ease of use. The American market is largely supplied by China, where manufacturers sell the devices on websites like Alibaba and directly to consumers, law enforcement officials say. Auto sears are often advertised as airsoft parts or tools and shipped with false documentation and packaging labels. They can also be created using a 3D printer. Once in a person’s hands, installation can take just seconds and requires scant technical knowledge or tools.

“It is so simple,” said Rick Vasquez, the former head of the ATF’s Firearms Technology Division. “The information is out there, and the knowledge to do it is out.” 

An auto sear installed on a Glock handgun. VICE News

Conversion devices can be installed in many types of handguns or rifles, but they’re particularly common for Glock pistols. That’s because of the Glock’s internal design, which makes its parts easy to access and modify. A Glock spokesperson did not respond to repeated requests for comment. 

In September, a Houston man opened fire with a Glock pistol modified with an auto sear after police showed up at his front door to arrest him on a narcotics warrant. One officer was killed and another wounded. Four months later, a convicted felon with a converted Glock wounded three more Houston officers in a gun battle in broad daylight. The suspect managed to escape, but police arrested him later that same day at his home, where they also found a cache of guns, machine gun components, and a 3D printer.

To gang members, auto sears are an advantageous new accessory that can inflict incredible damage and intimidate enemies, especially when paired with high-capacity magazines. One California ATF agent, who declined to be named because he was not authorized to speak on the agency’s behalf, said that in his first decade on the job, he hardly ever came across machine guns; now he sees firearms that have been converted with auto sears “all the time.” Some criminals, the agent added, have been caught with the devices on ghost guns — untraceable firearms that can be made at home or obtained without a background check.  

For nearly 90 years the federal government waged an aggressive campaign to shrink the pool of automatic weapons available to the public. 

In 1934, after several high-profile crimes involving machine guns, Congress passed the National Firearms Act, which required anyone who owned a fully automatic weapon to register it with the government and pay a $200 tax, equivalent to about $4,000 today. This significantly drove up the cost and difficulty of owning one. 

Industrious gunsmiths searched for workarounds. In the ’70s, conversion devices started surfacing in niche gun communities but the general public rarely sought them out. It became more difficult to obtain an auto sear in 1981, when the ATF ruled that possessing one was, in legal terms, the same as owning a machine gun, whether or not the device was installed on a firearm. Having an auto sear without the proper federal license, which requires an extensive background check and costly fees, can carry a 10-year federal prison sentence.

The auto sear overrides a handgun’s trigger bar, allowing it to fire multiple times with the single pull of a trigger.

Five years later, Congress passed the Firearms Owners Protection Act, blocking the import or manufacture of any new automatic weapons in the U.S. 

The 1986 law created an extremely limited pool of legal machine guns, and the weapons now command sky-high prices. Even basic models can cost $10,000 online. More sought-after weapons, like World War II-era machine guns, can run six figures. 

But obtaining an illegal machine gun is no longer so expensive or logistically challenging. Over the last five years, advances in low-cost manufacturing tools, like 3D printers, plus global commerce on the internet, have combined to create a vast black market of illegal machine gun makers, dealers, and traffickers. With an auto sear, anyone willing to break the law can effectively create a machine gun for as little as $20. 

Sales of auto sears have also been popularized by YouTubers and Instagrammers, whose demonstrations of the devices have racked up millions of views.

“People don’t sell drugs, for the most part, outside of the dark web — they’re not on Instagram selling crack cocaine or powder cocaine, but they are out there selling machine guns now,” said Boshek, the ATF agent in Dallas. 

Boshek said the wide availability of auto sears has created an arms race on the streets, and that his division in Texas is inundated with cases — including homicides and robberies — involving the devices. 

At the Ohio home of a self-described incel charged last July with plotting to massacre sorority members, sheriff’s deputies discovered a modified Glock machine gun stashed in a heating vent. In May 2021, federal agents in Florida seized two converted machine guns from a convicted felon linked to the murder of a 20-year-old mother. 

In Denver, when undercover ATF agents told arms traffickers they needed help outfitting a drug cartel “going to war” with its enemies, the blackmarket gun sellers quickly obliged. Over the course of a five-month investigation in 2018, traffickers working out of an auto-repair shop demonstrated their custom weaponry to the agents and showed them how to install and use auto sears and other automatic conversion devices. One trafficker extolled the devices as being “fuckin’ fast,” achieving ferocious rates of fire that caught him “by surprise.” They sold the agents a Glock handgun and five AR-15-style ghost guns. All the weapons had been modified into machine guns. “We go full-auto everything,” the traffickers said. 

“If you don’t have one, pretty much you’re butt naked,” said a former arms trafficker whose name has been withheld to protect his identity. He said demand for auto sears skyrocketed around 2020, as word got out on the street about the effectiveness of conversion devices. He claims to have modified and sold thousands of Glock machine guns, commanding between $500 and $3,000 per gun. 

He says the shooting death of a close friend motivated him to take his business above board and apply for a dealer license from the ATF.  

In 2019, the ATF opened an investigation into a Michigan resident who ordered auto sears through the mail. Agents say the man, a convicted felon on probation for selling machine guns, openly bragged about selling switches in a music video and ordered more than 20 conversion devices from a company located in Shenzhen, China. 

According to federal court documents, a separate investigation found that the company had sold auto sears to American customers 2,400 times over a 15-month period, for as cheap as $19.98 per device.

The U.S has become an increasingly lucrative market for auto sears. Many smugglers operate out of China, court records show, where conversion devices can be manufactured at low cost and shipped to American customers falsely labeled as innocuous items. In 2019, officials at Los Angeles International Airport intercepted more than 200 packages from China containing auto sears. The packages were labeled “multitool switch” or “screwdriver.” 

“It scares me for all of us,” said Nancy O’Malley, the district attorney for Alameda County in California. She says officers in her district have started coming across shipments of switches: “If there is a box of switches, then we know a modified weapon is in the community.”

Police and emergency vehicles on the scene of the November 2019 mass shooting in Fresno involving an auto sear that left ten people shot. Larry Valenzuela/Getty

The problem has prompted Homeland Security Investigations to form a task force with Customs and Border Protection, the United States Postal Inspection Service, the ATF, and Chinese counter-smuggling officials intended to stem the flow of auto sears from China into the U.S. 

“China is very good at identifying items, whether it be auto sears or sneakers, and expanding those markets to sell them,” said Joe Lestrange, the division chief of public safety and border security at Homeland Security Investigations. 

In 2019, the agency launched Operation TriggerFish, an initiative to track auto sear deliveries in the U.S. back to their points of origins. Homeland Security worked with international authorities to shut down production of switches in the Guangdong Province of China. It was a blueprint modeled after the government’s war on blackmarket fentanyl smuggling

Lestrange said that in the last three years, Homeland Security had seized 4,348 auto sears and opened up over 600 investigations related to the devices. While the agency regarded those seizures as successes, he said auto sears continue to show up in criminal investigations at an alarming rate. Stopping the flow of the devices, he added, depends on gathering new intelligence about how auto sears are entering the country. “We don’t know what we don’t know,” said Lestrange.

The spike in smuggling has pushed U.S. senators to ask for answers. In October 2021, Senators Amy Klobuchar and Cory Booker wrote a letter asking the Department of Justice how it plans to address overseas smuggling, as well as for statistics on seizures. 

Experts say auto sears are particularly sought after by anti-government extremists, who see amassing military grade weapons as a way to resist the government. 

In August 2020, an FBI agent posing as a foreign terrorist purchased a 3D-printed AR-15 auto sear from Timothy John Watson, a West Virginia man selling conversion devices as “portable wall hangers” online. According to court documents, authorities seized 903 conversion devices from Watson’s business, which had ties to the Boogaloo Boys.

One of those devices was sold to Steven Carrillo, a 32-year old Air Force staff sergeant and Boogaloo adherent who’d converted his homemade AR-15 into a machine gun. On May 29, 2020, during a protest in Oakland against the murder of George Floyd, Carrillo launched an ambush on two federal security officers, killing one. 

The following month, Carrillo struck again. He texted his fellow Boogaloo Boys to “kit up and get here,” before shooting at three California police officers when they arrived at this property. One was killed in the attack. 

A motorcade accompanies the hearse containing the coffin of Santa Cruz County Sheriff’s Sgt. Damon Gutzwiller, who was fatally shot by extremist Steven Carrillo. Shmuel Thaler/AP

Carrillo was apprehended by authorities after being wounded in the shooting, but not before he wrote “boog” in his own blood on the trunk of his stolen car. 

Rachel Rivas, a senior policy analyst at the Southern Poverty Law Center, said far-right and anti-government extremists seek machine guns because they are woven into much of their apocalyptic and conspiratorial ideology. 

“There is a worldview that there will be a coming moment in which they have to take up arms against the government and to do that they will need heavy weaponry,” she said. “It’s the ultimate symbol of personal freedom and individual rights; to the extreme.” 

Firearms are the weapon of choice for extremists to carry out violence. According to a recent report from the Anti-Defamation League, 75 percent of extremism-related deaths over the last decade were shootings.

 “It’s so much easier to have a full-auto firearm than to make weaponized anthrax,” said Mark Pitcavage, a senior research fellow at the ADL. He said that extremists represent a small sliver of criminal activity, but the types of attacks they carry out warrant concern. “You really do have to take it seriously. Some may argue it’s only a matter of time before we see one of these shooting sprees actually be conducted with full-auto weapons.”

Additional reporting by Brian Freskos