Gun Control and Statutory Interpretation: Controversy Over the ATF’s Ban on Bump Stocks

Alistair Simmons
Monday, March 6, 2023, 12:45 PM

The Bureau of Alcohol Tobacco, and Firearms Headquarters in Washington, D.C. (Mr.TinMD,; CC BY-ND 2.0,

Published by The Lawfare Institute
in Cooperation With

After the 2017 Las Vegas mass shooting, where a shooter using a firearm attachment called a bump stock killed 58 people and wounded approximately 500 more, the Bureau of Alcohol, Tobacco, Firearms of the Department of Homeland Security (“ATF”), amended their regulations to include bump stocks under the definition of machineguns. In announcing the new rule, the ATF noted that “such devices allow a shooter of a semiautomatic firearm to initiate a continuous firing cycle with a single pull of the trigger.” Previously, the ATF had taken a contrary position. The ATF’s reclassification gave them authority to ban bump stocks under the 1934 National Firearms Act and Gun Control Act which expressly bans “machineguns.” Owners of bump stocks were subsequently directed to dispose of their devices at ATF centers or face criminal penalties for unlawful possession.

Following the ATF’s statutory interpretation of bump stocks as machineguns, a contentious legal battle has emerged which strikes at the heart of the gun control and statutory flexibility controversy. Throughout multiple court cases, plaintiffs have alleged that the ATF abused its power by reinterpreting the relevant statute, challenging its revised definition of “machinegun.”

Circuit courts have since reached conflicting conclusions over the legality of the ATF’s ban, meaning that the Supreme Court will need to be the ultimate arbiter of this issue. In Gun Owners of America, Inc. v. Garland, the U.S. Court of Appeals for the Sixth Circuit upheld the ban by an equally divided en banc court (eight votes to uphold the ban; eight votes to strike it down). A unanimous panel of the U.S. Court of Appeals for the D.C. Circuit also ruled in favor of the government’s regulation in Damien Guedes v. ATF. But on Jan. 6 of this year, the U.S. Court of Appeals for the Fifth Circuit struck down the ban after siding with the plaintiffs in Cargill v. Garland. Ignoring the previous two decisions made by the Sixth Circuit on Dec. 3, 2021, and the DC Circuit on Aug. 9, 2022, the Fifth Circuit effectively reversed the ATF’s authority to regulate bump stocks. Since the Courts of Appeals—which rank second highest in authority—have issued contradictory opinions on the legality of the ATF’s bump stock ban, the case can only be resolved by the Supreme Court (though the Court has refused to consider challenges to the bump stock ban three times already).

The core legal dispute address three central questions: (1) Whether bump stocks can be interpreted under definition of the 1934 statute’s definition of “machinegun,” (2) whether the definition of machinegun under the National Firearms Act and Gun Control Act is ambiguous, and (3) whether the court should defer in favor of the government or plaintiff regarding ambiguity in the statue. This post unpacks each question by explaining the conclusions articulated in the differing decisions from each court case. Recognizing pivotal areas of contention between the court opinions offers insight into how the opposing parties will present their arguments in the Supreme Court, foreshadowing how the legal battle is likely to play out on the highest stage for domestic law.


First and foremost, there is disagreement over the National Firearms Act and Gun Control Act’s definition of “machinegun.” The statute defines it as such:

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.

Two key terms are central to interpreting the statue’s definition of machinegun: “automatically” and “single function of the trigger.”

In Damien Guedes v. ATF, the D.C Circuit Court interpreted “automatic” to mean a “result of a self-acting or self-regulating mechanism.” The ruling referenced the language of patents held by Slide Fire Solutions, which describes itself as the company of “the official bump stock.” Slide Fire’s patents define the technology as “[c]onvertible to full automatic.” The circuit court’s decision justified its interpretation of “automatic” with Slide Fire’s language. Further, the court noted that the plaintiffs had conceded during oral argument that a mechanical hand continuously moving a trigger attached to a semiautomatic gun would qualify as a machinegun. Therefore, the ruling reasoned, a device that aids in activating the trigger should be considered an automatic weapon.

The D.C Circuit Court interpreted the “single function of the trigger” to mean a “single pull of the trigger” and “analogous motions.” This interpretation is derived from the definition of a machinegun in Staples v. United States, where the Supreme Court referred to an “automatic” or “fully automatic” weapon under the National Firearms Act as one “that fires repeatedly with a single pull of the trigger.” Interpreting the definition to mean a “single pull of the trigger” is also consistent with precedent from Akins v. United States, where the Eleventh Circuit found the Bureau’s interpretation of “single function” as a “single pull of the trigger” to be consistent “with the statute and its legislative history.” The court’s definition emphasizes the action of squeezing the trigger as a “single function,” focusing on the users’ contact with the trigger rather than the movement of the trigger itself.

The D.C Circuit Court defended the logical significance of focusing on a person’s pull of the trigger rather than the mechanical process of the trigger moving back and forth as critical to the statute. If the interpretation of a “single pull of the trigger” was not used to interpret the National Firearms Act and Gun Control Act, the D.C Circuit Court argued, there would be loopholes in regulating machineguns:

Suppose that the weapon’s trigger would automatically move back and forth after the shooter’s initial pull of the trigger until the ammunition is spent, even if the shooter removes his trigger finger from the weapon during the firing sequence. Indeed, suppose that the shooter can stop the automatic firing sequence, should he so choose, by placing his trigger finger back on the weapon and contacting the automatically moving trigger. Under Plaintiffs’ strict understanding of the “single function of the trigger” to mean the mechanistic movement of the trigger itself, this weapon would evade classification as a machinegun even though the shooter’s initial pull of the trigger causes an automatic series of trigger movements and a resulting automatic series of shots, without any further input by the shooter whatsoever. 

In Cargill v. Garland, the Fifth Circuit interpreted “a single function of the trigger” as the mechanical “action of the trigger.” The court defines the action of a trigger to be a single oscillation—that is, each time a trigger moves back and forth from its original position. Although a bump stock enables the trigger to be pressed rapidly, it does not change the fact that one bullet is dispensed every time the trigger completes a cycle—therefore, the court reasoned, it is not a machinegun. Referencing a decision from the Navy-Marine Corps Court of Appeals, the court concluded that “the single act must be by the trigger… there is no mention of a shooter.”

The Fifth Circuit interpreted “automatic” to mean “self-acting.” The opinion argues that a bump stock is not self-acting because the shooter must maintain pressure on the back of the gun and trigger to continue the firing. In highlighting the difference between pulling a trigger and holding a trigger while pushing the back of a gun, the decision states, “Bump firing does not maintain if all a shooter does is initially pull the trigger.” The court concludes that a narrow interpretation of “automatic” based on the movement of the trigger is necessary because “the phrase ‘by a single function of the trigger’ modifies the adverb ‘automatically.’” Alluding to the argument made above, the ruling concludes that a gun can only be automatic if it dispenses multiple bullets per oscillation cycle of the trigger.

The core contention surrounding the definition of machinegun is whether the statute should be interpreted in consideration of the person using the gun or if interpretations should be purely mechanical and devoid of context. As a gun does not fire on its own, since it requires an operator to handle, an interpretation that disregards the input of the user will ignore the practical application of technologies that enhance the firing rate of guns. The debate over definitions is pivotal to determining the statutory authority of the ATF. Proving the viability of these competing definitions will tip the scales in favor of the prevailing side in a future court case.


In Gun Owners of America, Inc. v. Garland, the Sixth Circuit ruled that the “Chevron deference” framework could be applied to resolve the ambiguity within the definition of “machinegun.” The Chevron framework is introduced when a court concludes that Congress has not addressed the issue at hand and the statute is ambiguous regarding the matter. Under the Chevron framework, the court determines whether the “agency’s interpretation is based on a permissible construction of the statute.” The court applied the Chevron framework to conclude that the ATF’s rule reclassifying bump stocks as machineguns was based on a permissible construction of National Firearms Act and Gun Control Act. The Chevron framework provides more flexibility for executive agencies to reinterpret statutes.

In Damien Guedes v. ATF, the D.C Circuit Court interpreted bump stocks under the definition of “machinegun” to unambiguously support regulation. The Chevron framework was explicitly avoided by both sides, in the interests of avoiding such a polarizing topic. The court found its rulings consistent with previous cases, noting that “every circuit to have considered this question has so far upheld the Bump Stock Rule.”

In Cargill v. Garland, the Fifth Circuit Court found that the definition of the statute was simultaneously unambiguous and ambiguous. The ruling argues that the definition of machinegun unambiguously excludes bump stocks, but the definition is also too ambiguous for the courts to decide without Congress clarifying. The ruling articulates this two-pronged logic:

Nor can we say that the statutory definition unambiguously supports the Government’s interpretation. As noted above, we conclude that it unambiguously does not. But even if we are wrong, the statute is at least ambiguous in this regard. And if the statute is ambiguous, Congress must cure that ambiguity, not the federal courts.

This logic justifies any shortcomings in the ruling’s interpretations as a reason why the statute’s language is too ambiguous, so it cannot be remedied or enforced by the courts. In this case, both sides also explicitly denied addressing the Chevron framework issue.

Rule of Lenity

The Cargill v. Garland decision raises the importance of exercising the rule of lenity in deferring against criminal prosecution. The rule of lenity is the principle that ambiguous criminal law should lean against prosecuting defendants. Instead of resolving ambiguity through legal interpretation of the statute, the ruling conjures that the rule of lenity should let the statutory uncertainty remain unresolved so the owners of bump stocks are not punished. The opinion states:

Even if that conclusion were incorrect, the rule of lenity would still require us to interpret the statute against imposing criminal liability. A rich legal tradition supports the “well known rule” that “penal laws are to be construed strictly.” (cited United States v. Wiltberger.)

The Fifth Circuit Court deploys the rule of lenity to argue that the ATF’s ban on bump stocks should not be enforced because the language of the statute is not sufficiently clear. The court also argues that favoring against enforcement is necessary to maintain a division of power between the legislative and executive branches, implying that it is Congress’s burden to pass legislation that bans bump stocks.

The dissenting opinion in Cargill v. Garland refutes the majority’s decision favoring the rule of lenity to preserve the balance of powers. By rendering the regulatory capability of the ATF impotent, the decision to strike down the ban on bump stocks interferes with the democratic policies that established and protected the National Firearms Act and Gun Control Act. The dissent opinion states, “Invoking lenity to avoid all ambiguity thwarts the meaning of the text and substitutes our judgment for the People’s about what counts as a crime.” The rule of lenity can overstep judicial power by overriding the legislative ability to craft statues that effectively protect public policy (and safety) interests.

The dissenting opinion also cautions that the rule of lenity should only be invoked in extreme situations where the ambiguity is so great that discerning any reasonable interpretation is impossible. The dissenting opinion reiterates Supreme Court precedent:

the rule of lenity only applies, if, after considering text, structure, history, and purpose, there remains a grievous ambiguity or uncertainty in the statute such that the [c]ourt must simply guess as to what Congress intended.” Maracich v. Spears, 570 U.S. 48, 76 (2013) (emphases added) (cleaned up); see, e.g., Ocasio v. United States, 578 U.S. 282, 295 n.8 (2016) (similar); Robers v. United States, 572 U.S. 639, 646 (2014) (similar); United States v. Hayes, 555 U.S. 415, 429 (2009) (similar).

Gun Owners of America, Inc. v. Garland and Damien Guedes v. ATF echo the dissenting opinion’s sentiment that the rule of lenity should not be applied capriciously and should only be considered when all alternatives are exhausted.


As the most recent Fifth Circuit Court ruling has reignited contention within a prolonged legal dispute over the legality of bump stocks, it appears that the Supreme Court may soon have the momentous task of resolving this issue once and for all. Though the Supreme Court has consistently declined to hear challenges involving the ban, it is likely that the dispute will be reintroduced to the docket due to the overturning of precedent in Cargill v. Garland in January of this year. 

A Supreme Court decision on this matter would have significant implications. A ruling that upholds the ATF’s ban on bump stocks would advance protections for public safety by regulating semiautomatic guns that are modified to be automatic. An affirmative decision would also protect other executive agencies’ ability to reinterpret statutes to address emerging concerns. A ruling overturning the ban would effectively limit the ATF’s authority to regulate automatic weapons, offering loopholes that would make rapid-fire weapons more accessible and lawful. 

Alistair Simmons is an undergraduate researcher at Duke University's Sanford School of Public Policy and an artist and journalist.

Subscribe to Lawfare