In Garland v. Cargill, decided June 14, 2024, the Supreme Court ruled 6-3 that a bump stock does not turn a semi-automatic rifle into a machine gun under federal law. The decision struck down the 2018 federal regulation that had reclassified bump stocks as machine guns and required owners to destroy or surrender them. Bump stocks are once again legal under federal law, though 18 states still ban them independently.
What the Court Held
Justice Clarence Thomas wrote the majority opinion for six justices. The holding turned on the statutory definition of a machine gun, which since 1934 has covered any weapon that fires more than one shot automatically “by a single function of the trigger.”1Office of the Law Revision Counsel. 26 USC 5845 – Definitions The Court read that phrase mechanically. A “function of the trigger” is the physical movement of the trigger itself, rearward to release the hammer and forward to reset. A bump-stock-equipped rifle still requires that full cycle for every shot. It fires faster, but not from a single function.2Supreme Court of the United States. Garland v. Cargill
The majority also concluded the rifle does not fire “automatically” even under a broader reading. The shooter must maintain constant forward pressure on the handguard to sustain the cycle. Let go, and the firing stops. A bump stock, the Court wrote, “merely reduces the amount of time that elapses between separate ‘functions’ of the trigger.” Firing quickly is not firing automatically.
Justice Samuel Alito joined the majority and wrote a short concurrence acknowledging the policy tension. He noted “a simple remedy for the disparate treatment of bump stocks and machineguns. Congress can amend the law.” The message was direct: if bump stocks are to be banned, that job belongs to legislators, not to an agency reinterpreting a 90-year-old statute.
The Mechanical Question at the Center of the Case
A bump stock replaces the fixed stock on a semi-automatic rifle with a housing that lets the firearm slide back and forth. The shooter presses the rifle forward with the non-firing hand while keeping the trigger finger stationary against a ledge. When a round fires, recoil pushes the rifle rearward, pulling the trigger away from the finger and letting it reset. Forward pressure then slides the rifle back into the finger, pressing the trigger again.
The device has no springs, motors, or automated mechanism. It does not force the rifle to keep firing. It reshapes how the shooter’s hands interact with the weapon so the recoil itself paces rapid trigger presses. A standard AR-15 fires roughly five rounds per second; with a bump stock, seven to eight. A true automatic AR-15 fires about 15 rounds per second, emptying a 30-round magazine in under two seconds.
That gap between “faster semi-auto” and “actual automatic” is where the case was decided. The trigger still had to travel, release, and reset for each shot. That was enough to keep bump stocks outside the statutory definition.
The Dissent
Justice Sonia Sotomayor, writing for three justices, argued the majority ignored how the device actually operates in practice. In her view, a shooter who holds the rifle in bump-fire position and lets recoil do the rest has performed a single action producing continuous fire, which is what Congress meant to prohibit. The dissent framed the distinction between a moving trigger and a moving finger as a technicality the drafters never intended.
Why the Rule of Lenity Mattered
The decision was not only about trigger mechanics. It was also about who defines federal crimes. The rule of lenity requires courts to interpret genuinely ambiguous criminal statutes in a defendant’s favor, on the theory that people are entitled to fair warning from Congress about what conduct is illegal.
The stakes here were severe. The 2018 rule attempted to reclassify hundreds of thousands of legally purchased devices as prohibited machine guns.3Federal Register. Bump-Stock-Type Devices Violating the National Firearms Act carries up to ten years in federal prison and a fine of up to $10,000.4Office of the Law Revision Counsel. 26 USC 5871 – Penalties The ATF had itself concluded between 2008 and 2017 that most bump stocks were not machine guns, then reversed course after the 2017 Las Vegas shooting. The Court’s ruling reinforced that an agency cannot expand a criminal statute’s reach by shifting its interpretation of old text.
The decision landed alongside Loper Bright Enterprises v. Raimondo, issued two weeks later, which eliminated the Chevron doctrine of judicial deference to agency interpretations. Together, the two rulings narrowed the ATF’s room to stretch firearm definitions past their plain language.
What This Means for Bump Stock Owners Now
Under federal law, bump stocks are legal to own, buy, and sell. The 2018 rule requiring destruction or surrender is void. An estimated 520,000 bump stocks were in civilian hands when that rule took effect.3Federal Register. Bump-Stock-Type Devices
State law is a different matter. As of 2025, 18 states maintain independent bans on bump stocks, and Cargill did nothing to disturb them. The Court addressed only the federal statutory definition of a machine gun, not state authority to regulate firearm accessories. Penalties under state law range from misdemeanor possession, punishable by up to a year in jail, to felony charges carrying multi-year prison terms. If you own a bump stock or are thinking of buying one, check the current law in your state before assuming federal legality settles the question.
Ripple Effects on Other ATF Rules
Forced Reset Triggers
The reasoning in Cargill reached forced reset triggers quickly. The ATF had classified certain devices, including the Rare Breed FRT-15 and Wide Open Trigger, as machine guns. In July 2024, a federal district court in Texas held those devices are not machine guns under the National Firearms Act.5Bureau of Alcohol, Tobacco, Firearms and Explosives. Rare Breed Triggers FRT-15s and Wide-Open Triggers (WOTs) Return By June 2025, the government entered a settlement agreeing not to enforce machine gun laws against people possessing or transferring eligible forced reset triggers.
The settlement is narrow. It covers only specific FRT-15 and WOT models, and not devices held as evidence in criminal cases. It does not extend to auto sears, lightning links, or trigger control group travel reducers, which the ATF still treats as machine gun conversion tools. State law can also independently prohibit forced reset triggers.
Binary Triggers
Binary triggers fire one round when the trigger is pulled and a second when it is released. Because each pull and each release counts as a separate function of the trigger under the Cargill framework, binary triggers sit clearly outside the machine gun definition. They remain federally legal, though some states restrict them.
Stabilizing Pistol Braces
The ATF’s 2023 rule reclassifying pistols with stabilizing braces as short-barreled rifles ran into similar trouble. In August 2024, the Eighth Circuit struck it down as arbitrary and inconsistent, finding no clear standard for when a brace’s design would trigger the reclassification. The court reasoned on administrative law grounds rather than directly applying Cargill, but the decision reflects the same judicial skepticism toward ATF regulatory reach.
Can Congress Still Ban Bump Stocks?
Yes. Cargill did not hold that bump stocks are constitutionally protected. It held that the existing statute does not cover them. A new law explicitly banning bump stocks would be evaluated on its own terms, likely under the Second Amendment framework from New York State Rifle & Pistol Association v. Bruen, not under the definitional analysis that decided Cargill.
Legislators moved fast after the ruling. A Senate measure to ban bump stocks by statute was blocked within days when it could not secure unanimous consent. No standalone bump stock ban has passed either chamber since. Passing one would require majority support, or 60 votes in the Senate to overcome a filibuster. Until Congress acts, the federal machine gun definition applies only to weapons whose triggers genuinely function once to produce multiple shots, and bump stocks stay on the legal side of that line.