On April 11, more than 40 members of Congress signed a letter urging the Bureau of Alcohol, Tobacco, Firearms and Explosives to take action on the proliferation of the auto sear, a small device that makes a semiautomatic gun capable of emptying an entire magazine with a single pull of the trigger. 

Auto sears, as The Trace and VICE News reported in March, have become increasingly popular among criminals, and have been tied to dozens of shootings by extremists, mass shooters, and drug traffickers. This April, a gunman armed with a converted Glock handgun opened fire in downtown Sacramento leaving six dead and 12 wounded.

“The ATF is the primary federal regulator for firearms and should be playing quarterback here,” said Representative Jake Auchincloss, a Democrat from Massachusetts, who signed the letter. “They should be enforcing the law on the ground. But they should also be putting some of the liability for the misuse of these weapons —  if that misuse is predictable and apparent — onto the manufacturers.” 

In their letter, members of Congress asked the ATF to be more explicit in calling conversion devices illegal and to crack down on them. They’re also asking the agency to put a stop to the companies “pushing the legal limits on these devices.” But finding an effective solution may be difficult. Industry insiders and law enforcement officials interviewed for this story questioned whether the agency has the power to do more than it’s already doing. 

Machine guns have been subject to strict federal regulation for nearly 90 years. The National Firearms Act of 1934 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. These requirements significantly drove up the cost of owning a machine gun, and as a result ownership became rare. 

The auto sear was invented in the 1970s as a way for gunsmiths and hobbyists to fashion their own automatic weapons away from the watchful eyes of the government. With some elbow grease, an auto sear can convert popular semiautomatic rifles and handguns into machine guns. But in 1981, the ATF ruled that an auto sear is, legally, a machine gun. Without the proper licensing and taxes paid, possession of one of the devices is punishable with up to 10 years in prison. 

In the last decade, foreign manufacturers have started producing auto sears in large quantities and sending them to the U.S. According to Homeland Security Investigations, most of the devices originate from China. The devices are marketed online on popular social media platforms, ecommerce sites, and forums, and can cost as little as $20. 

Auto sears for Glock handguns, called “switches,” have become so popular that they’ve been name-dropped in rap songs and mailed to the company’s headquarters for repairs by unwitting customers, former employees told The Trace. The ATF said it recovered 1,500 converted weapons in 2021, up from just 300 the year before.

“If a shooter had a fully automatic weapon versus a semiautomatic weapon, that should scare the shit out of every parent out there,” said Senator Chris Murphy, a Democrat from Connecticut. 

Because auto sears are already technically regulated under federal law, some say the ATF needs to focus on enforcement.

“This isn’t a regulatory problem; it’s an enforcement problem,” said Brian Luettke, a retired ATF special agent. Luettke pointed to the agency’s historically thin roster of field agents as one possible reason these devices have proliferated. And he emphasized that the parts themselves can be difficult to identify.

Another approach would be for the ATF to regulate the other half of a converted machine gun: The gun itself. It’s a path that the agency has taken in the past. 

In the late 1970s and early ‘80s, law enforcement agencies started recovering huge numbers of converted RPB Industries SM10 pistols. The popular semiautomatic pistol was a near-perfect replica of the Mac-10 submachine gun, and by shaving down a small internal component with a steel file, it could be modified to fire on fully automatic. At nearly a quarter of the price, it became a hot commodity among drug traffickers.  

Law enforcement recovered at least a thousand of the machine guns in crimes across the nation by 1980. That same year, the ATF linked 60 of the guns to drug related murders in Florida alone. 

To curb the proliferation of these military-grade weapons, the ATF took an unprecedented step. It reclassified a handful of easily converted semiautomatic pistols and rifles as machine guns.  The ruling legally grandfathered the weapons already in circulation, but forced an ultimatum on their makers: Redesign future iterations to be less susceptible to automatic conversion or face selling them under the strict regulations of the National Firearms Act.

Many Democrats say that it’s well within the power of the agency to apply this same strategy to curb the proliferation of modern-day auto sears, like Glock switches, though Luettke and other firearm experts contacted for this story told The Trace that doing so would mean having to regulate dozens of other similarly easy-to-convert handguns.

“A Glock is the most popular handgun in the United States. I think the ATF should explore, as they have in the past, using their regulatory measures to force companies to change their designs or face stricter classifications,” said Representative Eric Swalwell a Democrat from California, who also signed the April letter. 

“If they know that their Glocks can be retrofitted with auto sears that easily, and they’re not preventing it with simple design changes, that becomes a product liability,” said Auchincloss. 

Firearm experts and law enforcement officials interviewed for this story acknowledged that the ATF still takes regulatory action against gunmakers to change the design of semiautomatic firearms or gun parts to prevent automatic conversions, if inconsistently.

In the early 2000s, the ATF allowed a product called the Akins Accelerator, a predecessor to the bump stock that increases a gun’s rate of fire, to go to market. But after agents discovered the attachment could enable Ruger rifles to fire roughly 800 rounds per minute, they reclassified the part as a machine gun.

In 2021, the agency ruled that the semiautomatic T36 rifle designed and sold by the Tampa-based boutique gunmaker TommyBuilt Tactical was a machine gun, after agents were able to install fully automatic parts in the gun’s receiver. The gun — which retailed for over $3,000 — did not include any fully automatic components as sold, according to the company’s owner, Tom Bostick.

The ATF’s process of modifying the gun effectively broke it, according to Bostick, and he said the agency offered no proof that the firearm successfully fired. When an expert consultant replicated the ATF’s conversion on his behalf, the gun would not fire consistently. Still, the ATF threatened to retrieve the rifles from Bostick’s customers unless he offered an exchange program — in this case a more than $200 upgrade for each customer. Bostick then had to build all future guns so that they would be less capable of accepting fully automatic parts. 

Months later, the large German gunmaker Heckler & Koch sought to import a batch of rifles that could be converted to fully automatic fire similarly to the T36. The ATF initially classified the gun as a machine gun and stopped the import, according to Bostick and another person with knowledge of the interuption, who asked to remain anonymous because they were not authorized to speak publicly about it. But after some back-and-forth with Heckler & Koch’s legal team, the ATF walked back its decision, and agreed to classify the gun as a semiautomatic weapon.

“What’s the difference with my gun,” Bostick asked. “It’s just easier for the ATF to go after low-hanging fruit, and they know it would have bled me dry to fight it.”

Heckler and Koch did not respond to requests for comment.

“ATF is always concerned by the criminal use of firearms, including the criminal use of machine gun conversion devices,” said an ATF spokesperson when asked how the bureau plans to deal with the influx of machine gun cases. However, the spokesperson declined to disclose if the ATF had talked to gunmakers whose products are popular for conversion, saying, “We are unable to comment on our communications with private individuals or companies regarding their firearms, including any firearms submitted to ATF for evaluation.”  

Norm Bergeron, another former ATF agent, said it’s true that the agency is reluctant to regulate large companies. “You have to have clout to go up against the U.S. government,” he said. “It really comes down to money. Money buys you lobbyists, it buys you attorneys.” 

Democrats believe that reluctance is in part due to the ATF’s perpetual leaderlessness over the last 16 years and its historically lean budget. 
Any regulatory agency without permanent leadership is vulnerable to not fully fulfilling its mission,” said Representative Bonnie Watson Coleman of New Jersey, a Democrat who also signed the congressional letter to the ATF in April. Watson Coleman said she believes a regulatory path like the one tried during the 1980s could curtail automatic conversions of particular firearms.

In April, the Biden administration announced Steve Dettelbach, a former U.S. attorney from Ohio, as its nominee to head the ATF. This is the second attempt the administration has launched in securing a head for the agency after pulling its nomination of David Chipman, a former ATF agent and gun violence prevention advocate, last fall. 

Additional reporting by Chip Brownlee