Is a bump stock a “machinegun?” The U.S. Supreme Court takes up the question

After the 2017 mass shooting on the Las Vegas strip—the worst in American history—many Americans learned the phrase “bump stock” for the first time. This week, the U.S. Supreme Court will hear a challenge to a federal rule defining bump stocks as machine guns prohibited by federal law.

The case, Garland v. Cargill, is not a Second Amendment constitutional challenge. Instead, it is a classic statutory interpretation challenge: Is a bump stock a “machinegun” as defined in 26 U.S.C. 5845(b) of the National Firearms Act?

At the heart of the case is a fundamental disagreement between the government and the challengers over how bump stocks operate.

A bump stock, according to the government, is a device that modifies a standard semiautomatic rifle. It replaces a rifle’s stock— the part of the rifle that rests against the shooter’s shoulder.

The Oct. 1, 2017, Las Vegas shootings occurred when the shooter, Stephen Paddock, fired from his hotel room on a crowd attending the Route 91 Harvest music festival. He had equipped his rifles with bump stocks that enabled the firing of more than 1,000 rounds, ultimately resulting in the deaths of 60 and the wounding of approximately 500.

Shortly after the Las Vegas mass shooting, the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) launched what is known as a “notice-and-comment rulemaking” to reconsider its earlier position that bump stocks were not “machineguns” within the law’s definition. During that period, it sought information about the devices.

Then-President Donald Trump also issued a memorandum directing ATF to move expeditiously on the rule making, and the agency in 2018 published a final rule. This time, the agency rule concluded bump stocks fell within the definition of “machineguns.”

Michael Cargill bought two bump stocks in 2018 and turned them in to ATF after the ATF rule was issued. He then challenged the rule in a lawsuit against the U.S. attorney general and ATF.

It is a federal crime to possess or transfer a machinegun. The law defines “machinegun” as follows:

     “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.”

The fight in the Supreme Court centers on two parts of the definition: “automatically” and “by a single function of the trigger.”

The U.S. solicitor general, representing ATF, argues that a rifle equipped with a bump stock satisfies the “single function of the trigger” requirement because, “when a shooter * * * pulls the trigger, that movement initiates a firing sequence that produces more than one shot.”

The firing sequence is “automatic,” ATF explains, “because the device harnesses the firearm’s recoil energy as part of a continuous back-and-forth cycle that allows the shooter to attain continuous firing after a single pull of the trigger.”

But Cargill’s attorney, Jonathan Mitchell (who argued on behalf of Trump in the recent case involving Trump’s eligibility for the presidency under Section 3 of the 14th Amendment), counters both of the government’s arguments.

Mitchell contends there is no “single function of the trigger” because “the trigger of the gun re-sets — and must be reactivated by the shooter — between every single shot that is fired from a bump stock–equipped weapon. And that means there is only one shot per ‘function’ of the trigger. A bump stock accelerates firing by causing repeated ‘functions’ of the trigger to occur in rapid succession; it does not produce multiple shots in response to a ‘single function’ of the trigger.”

Even assuming bump stocks enable a semi-automatic rifle to fire more than one shot “by a single function of the trigger,” Mitchell argues, “they do not do so ‘automatically’ because the shooter must continually thrust the barrel or front grip of the rifle forward with his non-trigger hand for each cartridge he wants to shoot, while simultaneously applying rearward pressure on the weapon with his trigger hand.”

A federal trial court ruled in favor of the government, as did a three-judge panel of the U.S. Court of Appeals for the Fifth Circuit. But the full appellate court granted rehearing and reversed 13-3.

The appellate court majority said that at a minimum “single function of the trigger” and “automatic” are “grievously ambiguous” terms. Because the statute was ambiguous the court said the “rule of lenity” applied and resolved the ambiguities in favor of Cargill.

The rule of lenity is a judicial doctrine in criminal law that says when a law is unclear or ambiguous, a court should apply it in a way that is most favorable to the defendant.

Not surprisingly, a number of friend-of-the-court briefs have been filed in the case. Gun rights organizations support Cargill; big cities, medical and family groups back the government. There are also briefs urging the court to clarify the rule of lenity.

The Biden Administration has pushed back against those groups suggesting a ban on bump stock devices would violate the Second Amendment. “But the Second Amendment allows the government to prohibit ‘dangerous and unusual weapons,’” the government states, citing its first and most recent Second Amendment rulings. “Machineguns are a paradigmatic example of such weapons.”

And it warns that adopting Cargill’s interpretation of the rule will make it easier to evade the law’s ban on new machine guns.

The case will be argued Wednesday, Feb. 28. Tune in to the arguments via the court’s website: www.supremecourt.gov.

Marcia Coyle is a regular contributor to Constitution Daily and PBS NewsHour. She was the Chief Washington Correspondent for The National Law Journal, covering the Supreme Court for more than 30 years.