Auto sears are devices that convert semi-automatic firearms, which are designed to fire one shot per trigger pull, into fully automatic machine guns, allowing a shooter to continue firing as long as the trigger is depressed and the gun has ammunition. In other words, with an auto sear (also known as a “machine gun conversion device,” or MCD), someone can fire an entire magazine’s worth of ammunition in mere seconds. Worse yet, auto sears are very easy to manufacture and can even be 3D printed, which is why these components — especially those designed by third parties for Glock pistols, known as “Glock switches” — are showing up at more and more crime scenes around the country.
Are Auto Sears Legal to Own?
Generally, no. Machine guns, and the parts used to create them, have been highly regulated since the passage of the National Firearms Act (NFA) of 1934. According to 26 U.S. Code § 5845(b), “The term ‘machinegun’ means any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger. The term shall also include the frame or receiver of any such weapon, any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machinegun, and any combination of parts from which a machinegun can be assembled if such parts are in the possession or under the control of a person” (emphasis added).
Everyday Americans can still legally own machine guns — but only after receiving approval from the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). Those who wish to own an NFA item like a machine gun must submit an application with their fingerprints and a passport-style photo, pay a $200 tax stamp, and notify the chief law enforcement officer in their area. After the ATF conducts an enhanced background check that can take several months to a year, the person may purchase and receive the machine gun from a licensed dealer.
However, the Firearms Owners’ Protection Act (FOPA) of 1986 also prohibits civilians from owning machine guns manufactured after May 19, 1986. (And due to scarcity, machine guns made before that date cost tens of thousands of dollars.) Thus, auto sears, which are relatively recent inventions, are generally illegal to own. Only federally licensed gun makers can produce new machine guns for military and law enforcement entities. Those who are caught with an unregistered machine gun face up to 10 years in prison and a $250,000 fine.
How Glock Switches Work
Glock switches are auto sears designed for use on Glock pistols. They attach to the back of a Glock’s slide and interfere with the internal trigger mechanisms to allow for fully automatic firing. It’s also important to note that these devices are not manufactured by Glock, even if they are branded or referred to as such.
In essence, the switch has a small protrusion called a “disconnector” that holds the Glock’s trigger bar down, allowing the striker to continue firing as the slide reciprocates with recoil. This produces a lot of wear and tear on the pistol’s smaller internal parts because they are not meant for this consistently high rate of fire, at roughly 1,200 rounds per minute.
However, some designs omit the selector entirely and only allow for fully automatic firing. These “backplate” auto sears don’t extend from the rear of the slide, making them harder to recognize.
AUTO SEARS FOR AR-15s
Many semi-automatic AR-platform weapons feature the same components as the U.S. military’s full-auto-capable M16 and M4 rifles, including bolt carriers. This is why it is so easy to install a drop-in auto sear (DIAS) and convert a semi-auto AR-15 into a fully automatic weapon. Though there are a variety of shapes and styles, every DIAS simply interferes with the trigger components to ensure that the bolt (like a Glock’s slide) can keep cycling on its own after every shot. These devices simply capture the hammer and allow the rifle’s bolt to re-cock the hammer for continued firing.
Other auto sears for AR-15s are simpler designs, including “lightning links” and “swift links,” which are illegal for civilians to own. But even a coat hanger can be used to convert an AR-15 into a fully automatic machine gun.
The rising tide of glock switches and auto sears
Many auto sears, including those designed for Glocks and AR-15s, are imported from China. In May 2019, a Topeka, Kansas, man was indicted for importing an undisclosed number of Glock switches from China for “$19 a piece.” According to one news report, the ATF “identified 4,000 converter switches smuggled into the U.S.” from China and have recovered more than 3,000 of them. “But hundreds from that shipment are still out there somewhere and being made by other manufacturers.”
Retailers have sold auto sears through websites like Wish.com, Ali Express, and even Amazon. But these devices are also being made here in the U.S. According to the ATF’s assistant special agent in charge for Los Angeles, “We have seen cases here in L.A. where these are manufactured at home or within a machine shop,” and 3D printing files for Glock switches and AR-15 auto sears are easy to find online. Searches using the terms “auto sear,” “swift link,” “lightning link,” and “Yankee Boogle” — a reference to the extremist boogaloo movement — yield several results on some of the largest and most popular 3D printing sites.
Popular 3D gun printers also use YouTube and Discord to showcase fully automatic weapons equipped with their auto sear designs, and some demonstrate how to 3D-print Glock and AR-15 auto sears.
In September 2020, two boogaloo supporters were charged with attempting to provide material support to Hamas, by delivering, in part, a 3D-printed auto sear. A month later, a West Virginia man was indicted for selling more than 600 auto sears for AR-15s that had been 3D printed. One of those auto sears ended up in the hands of a boogaloo supporter who was later arrested for murder in California.
The ATF seized 1,500 weapons modified with auto sears in 2021, a staggering increase over 2020, when only 300 were recovered. And in its most recent gun trafficking report, the ATF noted that it had recovered 814 machine gun conversion devices from 2012 to 2016, but that figure jumped to 5,454 from 2017 to 2021 — reflecting a 570% increase.
Other agencies offer similar reports. Washington, D.C.’s Metropolitan Police Department has recovered more crime guns with auto sears, seizing “20 auto sears in the District during the first half of 2021, double the number in the same time last year.” The rise in Glock switches has left Houston police feeling “terrified,” and law enforcement in Baton Rouge have seen “more than 80 cases over the past two years involving Glock switches or auto sears attached to weapons involved in crimes.”
Glock switches have been used in several mass shootings, including:
- Fresno, California, in November 2019
- Sacramento, California, in April 2022
- Chicago, Illinois, in May 2022
- Mobile, Alabama, in December 2022
- Dadeville, Alabama, in April 2023
- Boston, Massachusetts, in August 2023
- Chicago, Illinois, in October 2023
- Philadelphia, Pennsylvania, in March 2024
- Memphis, Tennessee, in April 2024
- Detroit, Michigan, in June 2024
- Birmingham, Alabama, in September 2024
- Tuskegee, Alabama, in November 2024
Glock has stated that it has “collaborated with law enforcement officials to target illegal sellers and users of switches” but has determined that, according to The New York Times, its pistols “cannot be altered” to “make it harder to attach switches.” Gun makers also continue to produce easily modified AR-15s and similar assault weapons, leaving law enforcement agencies — and the public at large — to face this growing problem on their own.