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Arm Braces

How gun makers exploited a device originally designed for disabled shooters

One of the weapons used in the Covenant School shooting in Nashville, Tennessee, in March 2023 was a Lead Star Arms Grunt AR-15 equipped with a pistol stabilizing brace — or simply “arm brace” — made by SB Tactical.1Palmetto State Armory, “Lead Star Arms Grunt 10.5” 5.56 AR-15 Pistol w/11” Grunt Handguard,” archived April 30, 2023, The firearm materially looks and operates like any other AR-15-style rifle, but the manufacturer sold it as if it was a “pistol,” and not a federally regulated short-barreled rifle (SBR).

The Covenant shooter's AR-15 shown with an SB Tactical SBA3 brace.
The Covenant School shooter’s Grunt AR-15 featured an SB Tactical SBA3 brace.

Arm braces have become a rallying cry among gun groups and gun enthusiasts, but arm-brace-equipped SBRs masquerading as “pistols” are a threat to public safety because they can fire faster, more powerful ammunition than traditional handguns while being easier to maneuver and hide on one’s person than full-size rifles. This is one reason why Congress enacted the National Firearms Act in 1934, making it more difficult for civilians to own short-barreled weapons — like the 12-inch-barreled Tommy guns and sawed-off shotguns used by gangsters of that era.

To date, at least four mass shootings have been committed with braced firearms, though the real number is likely higher, as arm braces are easy to mistake for shoulder stocks because of their similar appearance.

“Pistols” based on rifles

According to federal law, “The term ‘rifle’ means a weapon designed…and intended to be fired from the shoulder and designed…to use the energy of an explosive to fire only a single projectile through a rifled bore for each single pull of the trigger” (emphasis added), and since 1934, the NFA has required strict registration requirements for any rifle with a barrel less than 16 inches in length because of its concealability. SBRs are easy to hide under a person’s coat, in a backpack, or under a car seat, for example.

The NFA requires that civilians interested in owning an SBR first submit an application to the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) along with their fingerprints, a passport-style photo, and a $200 tax stamp before undergoing an enhanced background check. Only after being approved by the ATF can someone take possession of an NFA item.

Gun makers have spent years producing “pistol” versions of rifles, including AR-15s and AK-47s, with shorter barrels but lacking conventional shoulder stocks. But AR-style pistols in particular were quite unpopular in the past because their exposed buffer tubes — where a stock would normally be installed on rifle variants — prevented people from supporting these weapons against their shoulders while firing, making AR-style pistols very difficult to shoot.

That is until 2012, when Alex Bosco invented the first arm brace as a way to help disabled shooters fire an AR-15 pistol with just one hand. The ATF originally approved of the device for this use, saying that it did not turn an AR-15 pistol into an SBR on its own.

The first arm brace shown strapped to a shooter's forearm.
The first arm brace was made of foam rubber and wrapped around a shooter’s forearm. (ATF Photo)

But gun enthusiasts quickly realized that they could shoulder arm braces to shoot AR-style pistols more accurately. It didn’t take long for the gun industry — including the company that Bosco co-founded, SB Tactical, as well as manufacturers Maxim Defense, Shockwave Technologies, and Magpul, among others — to begin creating arm braces that look and can be operated just like shoulder stocks for a wide range of “large-format pistols,” as they are known, allowing people to take advantage of regulatory failures and acquire theses firearms without going through the NFA registration or enhanced background check process.


In January 2015, the ATF published an open letter stating that the original arm brace’s classification was “based upon the use of the device as designed. When the device is redesigned for use as a shoulder stock on a handgun with a rifled barrel under 16 inches in length, the firearm is properly classified as a [short-barreled rifle] under the NFA.” Then, in March 2017, the agency sent a letter to SB Tactical, stating that as long as an arm brace was not designed or marketed to be used as a shoulder stock, its “sporadic, situational” shouldering by an end-user would not necessarily “redesign” the host weapon to create an SBR.

This created an opening for the gun industry, which seized on the 2017 “reversal” letter. Soon, larger manufacturers began offering brace-equipped firearms, and gun enthusiasts could also purchase standalone arm braces to retrofit the pistols they already owned or build new ones. In April 2018, SB Tactical unveiled what would become its most popular brace, the SBA3, which looks and is capable of functioning like a typical collapsible stock for an AR-15 and offers very little support for one-handed shooting. As mentioned, the SBA3 was also used in the Boulder and Nashville mass shootings.

As arm braces evolved and became more popular — the ATF estimates that 3 million braces were purchased by 1.4 million gun owners — more showed up at crime scenes. In the intervening years, the ATF repeatedly attempted to address arm braces through determination letters and rulemaking. In August 2020, the ATF ordered gun maker Q LLC to cease and desist selling its Honey Badger Pistol, which featured a proprietary SB Tactical arm brace, because of its resemblance to the company’s Honey Badger SBR. But after facing a backlash from the gun lobby,6See NRA-ILA, “Your Action Needed: Urge the Department of Justice to Rein in ATF’s Arbitrary Determination on “Honey Badger” Pistol!” October 6, 2020,; Firearms Policy Coalition, “FPC Statement on ATF’s Cease and Desist to Q, LLC Regarding the Honey Badger Pistol’s Status as a Purported Short Barrel Rifle,” October 6, 2020,; and Gun Owners of America, “GOA: Tell Trump to Reverse ATF’s Reclassification of Honey Badger Pistol,” Firearms News, October 8, 2020, the Department of Justice suspended the cease-and-desist order against Q LLC just two months later.

The Honey Badger Pistol shown next to the Honey Badger SBR.
Note the “arm brace” on the Honey Badger Pistol (top) and the stock on the Honey Badger SBR (bottom). (ATF Photo)

In December 2020, the ATF published its “Objective Factors for Classifying Weapons with ‘Stabilizing Braces,’” outlining the factors that the ATF intended to look at in determining which brace-equipped weapons are pistols and which are SBRs going forward, including the weapon’s dimensions and how the gun is marketed. The ATF was essentially trying to make its private determination process public, but after another backlash from gun groups,7See Chris Eger, “Under Pressure, ATF Rescinds Pistol Brace Notice,” December 24, 2020,; Gun Owners of America, “Take Action to Protect Gun Owners from a Rogue ATF,” December 21, 2020,; and Firearms Policy Coalition, “BREAKING: ATF to Issue Guidance on ‘Stabilizing Braces,’” December 16, 2020, the agency withdrew the proposed rule.

Weeks after the Boulder shooting, in April 2021, the Biden administration announced several executive actions to combat gun violence, including ordering the Department of Justice to clarify the law as to deadly arm-braces. In June, the ATF proposed a rule to clarify which brace-equipped weapons qualify as SBRs using a worksheet awarding points for various factors, such as a gun’s dimensions and configuration, showing that the brace-equipped firearm is suited for one-handed operation (like a pistol) or shoulder firing (like a rifle). If the weapon was deemed an SBR using the worksheet, gun owners could remove the brace, install a longer barrel, turn the weapon in, or register it as an SBR through the usual NFA application process.

Once the rule became available for public comment, several gun groups “created campaigns to organize their members in opposition to the rule,” driving tens of thousands of negative comments, yet the ATF persisted. In January 2023, the agency published its final rule for “Factoring Criteria for Firearms with Attached ‘Stabilizing Braces,’” which did away with Worksheet 4999 and amended the federal definition of “rifle” to include arm-brace-equipped weapons where 1) the brace “provides surface area that allows the weapon to be fired from the shoulder” and 2) other factors, such as the weapon’s dimensions and marketing, show the gun was designed and intended to be fired from the shoulder. In other words, arm braces by themselves aren’t touched by the final rule, but adding one to a weapon may create an SBR.

The final rule also provided a 120-day amnesty period that ended on May 31, 2023, for those who already own brace-equipped weapons and wished to register them as SBRs without paying the usual $200 tax stamp. Owners could also remove the braces from their weapons, install longer barrels, or turn the firearms in to law enforcement.

Since the final rule was announced, several lawsuits have been filed against the ATF, alleging that the rule infringes upon the Second Amendment and that the agency tasked with enforcing the NFA illegally expanded its authority to close the loophole that has aided criminals. The plaintiffs include gun groups, such as the NRA, and arm brace makers like SB Tactical and Maxim Defense. The gun lobby’s resistance even led to an effort by House Republicans to overturn the rule through the Congressional Review Act. The House passed the resolution by a slim margin on June 13, 2023, days after the arm brace rule’s amnesty period ended, but the Senate voted against it on June 22.