RECOMMENDED FOR PUBLICATION

Pursuant to Sixth Circuit I.O.P. 32.1(b)

File Name: 23a0086p.06

UNITED STATES COURT OF APPEALS

FOR THE SIXTH CIRCUIT

SCOTT A. HARDIN,

Plaintiff-Appellant,

v.

BUREAU OF ALCOHOL, TOBACCO, FIREARMS AND 

EXPLOSIVES, an agency of the Department of Justice; 

STEVEN M. DETTELBACH, Director Bureau of Alcohol, 

Tobacco, Firearms, and Explosives; UNITED STATES 

OF AMERICA; MERRICK B. GARLAND, Attorney 

General, in his official capacity as Attorney General of 

the United States,

Defendants-Appellees.

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No. 20-6380

Appeal from the United States District Court for the Western District of Kentucky at Louisville.

No. 3:19-cv-00056—David J. Hale, District Judge.

Argued: January 19, 2023

Decided and Filed: April 25, 2023

Before: GILMAN, McKEAGUE, and BUSH, Circuit Judges.

_________________

COUNSEL

ARGUED: Jason Todd Hardin, HARDIN LAW, PLLC, Louisville, Kentucky, for Appellant. 

Brad Hinshelwood, UNITED STATES DEPARTMENT OF JUSTICE, Washington, D.C., for 

Appellees. ON BRIEF: Jason Todd Hardin, HARDIN LAW, PLLC, Louisville, Kentucky, 

J. Allan Cobb, COBB LAW PLLC, Louisville, Kentucky, for Appellant. Brad Hinshelwood, 

Abby C. Wright, Kyle Edwards, UNITED STATES DEPARTMENT OF JUSTICE, 

Washington, D.C., for Appellees.

GILMAN, J., delivered the opinion of the court in which McKEAGUE, J., joined. 

BUSH, J. (pp. 10–13), delivered a separate opinion concurring in the judgment.

>
No. 20-6380 Hardin v. ATF, et al. Page 2

_________________

OPINION

_________________

RONALD LEE GILMAN, Circuit Judge. The placement of a bump stock on a 

semiautomatic rifle causes the rifle to function essentially like a machinegun by dramatically 

increasing the rate of fire. And the possession of a machinegun is a criminal offense under the 

Gun Control Act of 1968. This raises the question of whether a bump stock is a machinegun 

“part” as defined by the National Firearms Act of 1934. The question is a close one on which 

reasonable jurists have disagreed, a disagreement caused by ambiguities in how the applicable 

statute defines the term “machinegun.”

An Act of Congress could clear up the ambiguities, but so far Congress has failed to act. 

The Bureau of Alcohol, Tobacco, Firearms and Explosives (the ATF) has been on both sides of 

this issue, with its current regulation (the Rule) banning bump stocks as a machinegun part. In 

this situation, the rule of lenity that is applicable to criminal offenses requires us to rule in favor 

of Hardin. We therefore REVERSE the judgment of the district court and REMAND for 

further proceedings consistent with this opinion.

I. BACKGROUND

The Gun Control Act provides that “it shall be unlawful for any person to transfer or 

possess a machinegun.” 18 U.S.C. § 922(o)(1). It incorporates by reference (see id.

§ 921(a)(24)) the definition of a machinegun as set forth in the National Firearms Act, which 

reads 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.

26 U.S.C. § 5845(b).
No. 20-6380 Hardin v. ATF, et al. Page 3

For over a decade, the ATF, to which Congress has delegated the authority to administer 

the National Firearms Act and the Gun Control Act, maintained that a bump stock is not a 

machinegun part. But in 2018, after a gunman in Las Vegas, Nevada used bump stocks attached 

to semiautomatic rifles to kill 58 people and injure roughly 500 more in the span of 

approximately 10 minutes, the ATF reversed its position by promulgating the Rule. The Rule 

gave possessors of bump stocks 90 days from its effective date during which to destroy or 

abandon their bump stocks, after which they would be in violation of the Gun Control Act’s 

prohibition on machineguns and their parts. See Bump-Stock-Type Devices, 83 Fed. Reg. 

66,514 (Dec. 26, 2018).

The appellant in this case, Scott Hardin, owned several bump stocks. Following the 

ATF’s promulgation of the Rule, Hardin brought an action in the Western District of Kentucky, 

challenging the Rule as exceeding the ATF’s statutory authority. The district court granted the 

ATF’s motion for judgment on the administrative record. Hardin now appeals.

II. ANALYSIS

Whether a bump stock is a machinegun part depends on how one interprets the definition 

of a machinegun as set forth in the National Firearms Act. In particular, the dispute focuses on 

the words “automatically” and “a single function of the trigger.” Those courts of appeals that 

have faced the issue are divided on the answer, and the Supreme Court has not weighed in. On 

one side, saying that a bump stock is included within the definition of a machinegun, are the 

Tenth Circuit and the D.C. Circuit. See Aposhian v. Barr, 958 F.3d 969 (10th Cir. 2020), aff’g

374 F. Supp. 3d 1145 (D. Utah 2019), en banc reh’g order vacated as improvidently granted, 

989 F.3d 890 (10th Cir. 2021) (en banc), cert. denied, 143 S. Ct. 84 (2022); Guedes v. Bureau of 

Alcohol, Tobacco, Firearms and Explosives, 920 F.3d 1 (D.C. Cir. 2019) (per curiam), aff’g 356 

F. Supp. 3d 109 (D.D.C. 2019), cert. denied, 140 S. Ct. 789 (2020). The opposite view is taken

by the Fifth Circuit. See Cargill v. Garland, 57 F.4th 447 (5th Cir. 2023) (en banc), rev’g

20 F.4th 1004 (5th Cir. 2021), and Cargill v. Barr, 502 F. Supp. 3d 1163 (W.D. Tex. 2020), 

petition for cert. filed (Apr. 7, 2023). And our own circuit is split down the middle, with eight 

judges voting to uphold the Rule and eight judges voting to strike it down. See Gun Owners of 

Am., Inc. v. Garland, 19 F.4th 890 (6th Cir. 2021) (en banc), vacating by an equally divided 
No. 20-6380 Hardin v. ATF, et al. Page 4

court 992 F.3d 446 (6th Cir. 2021), and aff’g by an equally divided court Gun Owners of Am., 

Inc. v. Barr, 363 F. Supp. 3d 823 (W.D. Mich. 2019), cert. denied, 143 S. Ct. 83 (2022).

A total of 22 opinions are set forth in the above-cited cases, which fully explore all 

aspects of the issue in nearly 350 pages of text. We therefore have the benefit of being able to 

draw our own conclusions from these erudite opinions without having to repeat them verbatim.

A. The weight of authority concludes that the definition of a machinegun is 

ambiguous as applied to a bump stock

Hardin argues that the statutory definition of a machinegun unambiguously excludes 

bump stocks, whereas the ATF argues that the best reading of the statute compels the opposite 

conclusion. Without repeating the intricacies of those positions here, there can be no doubt that a 

significant number of reasonable jurists have reached diametrically opposed conclusions as to 

whether the definition of a machinegun includes a bump stock.

The viability of competing interpretations is exemplified not only by the myriad and 

conflicting judicial opinions on this issue, but also by the ATF’s own flip-flop in its position. 

And because the statute is “subject to more than one reasonable interpretation,” it is ambiguous. 

See Donovan v. FirstCredit, Inc., 983 F.3d 246, 256 (6th Cir. 2020) (quoting N. Fork Coal Corp. 

v. Fed. Mine Safety & Health Comm’n, 691 F.3d 735, 740 (6th Cir. 2012)); see also N. Fork 

Coal Corp., 691 F.3d at 740 (“Although both parties argue that the statutory language is plain 

and unambiguous, both also argue that the plain meaning supports their interpretation. This 

indicates ambiguity. Furthermore, the existence of divergent court opinions also suggests 

ambiguity.” (quoting Pugliese v. Pukka Dev., Inc., 550 F.3d 1299, 1304 (11th Cir. 2008))).

B. The Chevron doctrine is inapplicable in the present case

Under what has become known as Chevron deference, “a court review[ing] an agency’s 

construction of the statute which it administers . . . is confronted with two questions.” Chevron, 

USA, Inc. v. NRDC, 467 U.S. 837, 842 (1984):

First, always, is the question whether Congress has directly spoken to the precise 

question at issue. If the intent of Congress is clear, that is the end of the matter; 

for the court, as well as the agency, must give effect to the unambiguously 

expressed intent of Congress. If, however, the court determines Congress has not 
No. 20-6380 Hardin v. ATF, et al. Page 5

directly addressed the precise question at issue, the court does not simply impose 

its own construction on the statute, as would be necessary in the absence of an 

administrative interpretation. Rather, if the statute is silent or ambiguous with 

respect to the specific issue, the question for the court is whether the agency’s 

answer is based on a permissible construction of the statute.

Id. at 842-43. Having determined that the statutory language is ambiguous, we would typically 

apply Chevron deference to uphold the Rule so long as it was not “arbitrary, capricious, or 

manifestly contrary to the statute.” See id. at 844.

But both parties urge us to determine the legality of the Rule without relying on Chevron

deference. The government has not invoked Chevron deference, believing that “it is unnecessary 

to consider what level of deference, if any, the rule should be accorded.” And Hardin’s view is, 

first, that the government has waived the application of Chevron deference and, alternatively, 

that Chevron deference is inapplicable when the underlying statute carries the possibility of 

criminal sanctions. We need not resolve the question of whether the government can waive the 

application of Chevron deference because we conclude that the statutory scheme before us is one 

that does not warrant the application of such deference.

The Supreme Court has not clearly identified the bounds of Chevron deference with 

respect to an agency’s construction of a statute with criminal applications. To be sure, Chevron

itself involved a statute whose violation could incur criminal penalties. See id. at 840; 42 U.S.C. 

§ 7413(c)(1) (1982). And in Babbitt v. Sweet Home Chapter of Communities for a Greater 

Oregon, 515 U.S. 687 (1995), the Supreme Court applied Chevron deference to the agency’s 

statutory interpretation notwithstanding the challengers’ argument that such deference was 

inappropriate because the statute included criminal penalties for certain violations. See id. at 

703-704 & 704 n.18.

The Supreme Court, however, has “never held that the Government’s reading of a 

criminal statute is entitled to any deference.” United States v. Apel, 571 U.S. 359, 369 (2014). 

This language was repeated in Abramski v. United States, 573 U.S. 169, 191 (2014), where the 

Supreme Court further noted that “criminal laws are for courts, not for the Government, to 

construe.”
No. 20-6380 Hardin v. ATF, et al. Page 6

The reasons to exercise caution in applying Chevron deference to an agency’s 

construction of a statute with criminal applications are persuasive. Among the primary rationales 

for Chevron deference are: (1) “that agencies are more likely to get the answer right, given their 

expertise,” Arangure v. Whitaker, 911 F.3d 333, 341 (6th Cir. 2018), and (2) “that ‘policy 

choices’ should be left to Executive Branch officials ‘directly accountable to the people,’” Epic 

Sys. Corp. v Lewis, 138 S. Ct. 1612, 1630 (2018) (quoting Chevron, 467 U.S. at 865).

These rationales, however, have less force in the context of laws imposing criminal 

sanctions. “[B]ecause of the seriousness of criminal penalties, and because criminal punishment 

usually represents the moral condemnation of the community, legislatures . . . should define 

criminal activity.” United States v. Bass, 404 U.S. 336, 348 (1971). Moreover, we “feel deep 

discomfort at allowing an agency to define the very criminal rules it will enforce.” Aposhian 

v. Wilkinson, 989 F.3d 890, 900 (10th Cir. 2021) (Tymkovich, J., dissenting from the denial of 

rehearing en banc). Such a scheme “raises serious constitutional concerns by making [the] ATF 

the expositor, executor, and interpreter of criminal laws.” Id. (emphasis in original).

On the other hand, “we must interpret [a] statute consistently, whether we encounter its 

application in a criminal or noncriminal context.” Leocal v. Ashcroft, 543 U.S. 1, 11 n.8 (2004); 

see also, e.g., United States v. Thompson/Center Arms Co., 504 U.S. 505, 517-18 (1992) 

(applying a rule of statutory construction that is ordinarily applicable only in criminal cases to a 

tax statute because the statute, which also had criminal applications, had to be interpreted 

consistently across both the civil and criminal domains). A bright-line rule that Chevron

deference cannot be applied to agency constructions of statutes with criminal consequences 

would therefore preclude the application of Chevron deference to “statutes that bear both civil 

and criminal applications,” “[a] category that covers a great many (most?) federal statutes 

today.” See Gutierrez-Brizuela v. Lynch, 834 F.3d 1142, 1156 (10th Cir. 2016) (Gorsuch, J., 

concurring); see also Gun Owners of Am., Inc. v. Garland, 19 F.4th 890, 924-25 (6th Cir. 2021) 

(en banc) (Murphy, J., in support of striking down the Rule) (“[A]ny distinction between ‘pure’ 

criminal laws and ‘hybrid’ civil-criminal laws is a mirage.”). In light of the “one statute, one 

interpretation rule” gleaned from Leocal and Thompson, as well as the Supreme Court’s lack of 
No. 20-6380 Hardin v. ATF, et al. Page 7

clarity with respect to the application of Chevron deference to statutes that carry criminal 

penalties, we decline to adopt such bright-line rules in either direction.

Instead, we conclude that the particular statutory scheme before us is not an appropriate 

one to apply Chevron deference. We so hold because the statutory scheme is predominantly 

criminal in scope and because of the nature of the actions that it criminalizes.

First, the Gun Control Act prohibits anyone from transferring or possessing a 

machinegun. 18 U.S.C. § 922(o)(1). A knowing violation of this provision is punishable by up 

to 10 years of imprisonment. Id. § 924(a)(2). The civil implications of the Rule are, by contrast, 

“quite limited.” Aposhian, 989 F.3d at 905 (Eid, J., dissenting from the denial of rehearing en 

banc):

The [Gun Control Act’s] prohibition on “machineguns” is subject to only two 

extremely limited exceptions, for “machineguns” (1) “transfer[red] to or by, or 

possess[ed] by or under the authority of” the federal or a state government, 

[18 U.S.C.] § 922(o)(2)(A), or (2) lawfully possessed before the prohibition went 

into effect, id. § 922(o)(2)(B). Only “machineguns” that fall within these narrow 

exceptions are subject to civil consequences, and even then, the civil 

consequences are limited—the chief consequence is a registration requirement. 

See 26 U.S.C. §§ 5841, 5845(a), (b).

Id. (second and third alterations in original). Thus, “[g]iven the breadth of the criminal 

prohibition and the limited nature of the exceptions giving rise to civil ramifications,” id., we 

conclude that the statutory scheme has a predominantly criminal scope.

Second, we perceive of no special expertise possessed by the ATF with respect to the 

construction of this statutory scheme that the judiciary lacks:

The special deference required by Chevron is based on the expertise of an 

administrative agency in a complex field of regulation with nuances perhaps 

unfamiliar to the federal courts. Unlike environmental regulation or occupational 

safety, criminal law and the interpretation of criminal statutes is the bread and 

butter of the work of federal courts.

Dolfi v. Pontesso, 156 F.3d 696, 700 (6th Cir. 1998) (citation omitted). As noted by our 

colleague Judge White, “we have highly technical and complex securities, tax, workplace safety, 

and environmental-law regimes in which the applicable agency exercises delegated authority to 
No. 20-6380 Hardin v. ATF, et al. Page 8

promulgate regulations fleshing out statutory provisions—regulations that have both civil and 

criminal applications.” Gun Owners of Am., Inc., 19 F.4th at 902 (White, J., in support of 

upholding the Rule). But unlike securities, tax, workplace safety, and environmental-law 

regimes, which include criminal penalties for uniquely regulatory crimes, there is nothing highly 

technical or complex about condemning, for example, the distribution of dangerous drugs, the 

commission of violent acts, or, as relevant here, the possession of deadly weapons. These are 

areas in which the courts are well-equipped to operate, and we see no reason why we should 

abdicate our interpretive responsibility in such instances. We therefore decline to afford 

Chevron deference to the ATF’s construction of the term “machinegun.” 

C. The rule of lenity requires us to rule in Hardin’s favor

This brings us to the rule of lenity, under which “penal statutes are to be construed 

strictly.” FCC v. Am. Broad. Co., 347 U.S. 284, 296 (1954). Therefore, when Chevron

deference is not warranted and standard principles of statutory interpretation “fail to establish 

that the Government’s position is unambiguously correct[,] we apply the rule of lenity and 

resolve the ambiguity in [the criminal defendant’s] favor.” United States v. Granderson, 

511 U.S. 39, 54 (1994). “In sum, it is not enough to conclude that a criminal statute should cover 

a particular act. The statute must clearly and unambiguously cover the act.” Cargill v. Garland, 

57 F.4th 447, 473 (5th Cir. 2023) (en banc) (Ho, J., concurring) (emphases in original).

Judge Ho’s concurrence in Cargill directs our attention to two persuasive analogies. See 

id. at 473-74, 478. The first concerns designer drugs, which, although “just as lethal” as drugs 

prohibited by the Controlled Substances Act of 1970, “differed in chemical composition.” Id. at 

473. “Yet all three branches agreed that existing law did not ban designer drugs,” requiring 

Congress to enact the Controlled Substance Analogue Enforcement Act of 1986. Id. at 473-74. 

The second analogy concerns the facts of United States v. Wiltberger, 18 U.S. 76 (1820). See 

Cargill, 57 F.4th at 478 (Ho, J., concurring). In that case, the Supreme Court “unanimously 

construed a statute that punished manslaughter on the ‘high seas’ not to apply to an identical act 

on a river. The Court noted that it was ‘extremely improbable’ Congress would want to treat 

upstream manslaughter differently from manslaughter committed downstream, past the river’s 

mouth.” Id. (quoting Wiltberger, 18 U.S. at 103-06). Even so, the Supreme Court ruled in the 
No. 20-6380 Hardin v. ATF, et al. Page 9

criminal defendant’s favor on the basis that “probability is not a guide which a court, in 

construing a penal statute, can safely take.” Wiltberger, 18 U.S. at 105.

“Bump stocks may well be indistinguishable from automatic weapons for all practical 

purposes. But . . . ‘[i]t would be dangerous . . . to punish a crime not enumerated in the statute, 

because it is of equal atrocity, or of kindred character, with those which are enumerated.’” 

Cargill, 57 F.4th at 478 (Ho, J., concurring) (second ellipses in original) (quoting Wiltberger, 18 

U.S. at 96). Because the relevant statutory scheme does not clearly and unambiguously prohibit 

bump stocks, we are bound to construe the statute in Hardin’s favor.

III. CONCLUSION

For all of the foregoing reasons, we REVERSE the judgment of the district court and 

REMAND for further proceedings consistent with this opinion.
No. 20-6380 Hardin v. ATF, et al. Page 10

_______________________________________

CONCURRING IN THE JUDGMENT

_______________________________________

JOHN K. BUSH, Circuit Judge, concurring in the judgment. I agree that the district 

court’s judgment should be reversed. At a minimum, as the majority opinion holds, the National 

Firearms Act of 1934 admits of an interpretation that excludes a bump stock from the definition 

of a “part” of a “machinegun” under that statute. Indeed, this is the original interpretation that 

the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) gave to the statute. See ATF 

Rule 2006-2 at 2; 27 C.F.R. §§ 478.11 (2014), 479.11 (2016). That ATF later changed its views 

in order to ban bump stocks does not render unreasonable the ATF’s first reading of the statute. 

Indeed, the ATF’s first take aligns with the views of numerous judges on this court and 

elsewhere who have considered the relevant statutory text. See, e.g., Gun Owners of Am., Inc. v. 

Garland, 19 F.4th 890, 910 (6th Cir. 2021) (Murphy, J., dissenting), cert. denied, 143 S. Ct. 83 

(2022); Cargill v. Garland, 57 F.4th 447 (5th Cir. 2023) (en banc), petition for cert. filed (April 7, 

2023). Therefore, even accepting (as does the majority opinion) that the statute could reasonably 

be read either way as to the legality of bump stocks, the statute must be read under the rule of 

lenity to exclude a bump-stock rifle from the definition of a machinegun. See United States v. 

Granderson, 511 U.S. 39, 54 (1994); Jones v. United States, 529 U.S. 848, 858 (2000) (if there 

are two possible “readings of what conduct Congress has made a crime,” the “harsher 

alternative” reading should be rejected because “Congress should have spoken in language that is 

clear and definite”) (quoting United States v. Universal C.I.T. Credit Corp., 344 U.S. 218, 221–

22 (1952)). That is the import of the majority’s reasoning.

But I would go further. As explained by Judge Murphy in Gun Owners of America, Inc.

v. Garland, the best reading of the statute is that Congress never gave the ATF “the power to 

expand the law banning machine guns through [the] legislative shortcut” of the ATF’s rule at 

issue in this appeal, see Bump-Stock-Type Devices, 83 Fed. Reg. 66,514 (Dec. 26, 2018) (the 

Rule). See 19 F.4th at 910 (Murphy, J., dissenting). Simply put, under the statute as it currently 

reads, the addition of a bump stock to a rifle clearly does not make it a machinegun. 
No. 20-6380 Hardin v. ATF, et al. Page 11

Though my reasoning differs somewhat from the majority opinion, all judges on this 

panel agree on this point: it is up to Congress, not the ATF, to change the law if bump stocks are 

to be made illegal.

I.

This case turns on whether a bump stock is a “part” of a “machinegun” as used in the 

National Firearms Act. The relevant statutory provision reads: 

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.

26 U.S.C. § 5845(b). Under this definition, a bump stock cannot be a machinegun part because a 

bump stock by itself cannot increase the rate of fire of a rifle, nor does it change the mechanics 

of a “single function of the trigger.” 

The ATF’s brief provides clarity on how bump stocks operate. A “bump stock channels 

the recoil from the first shot into a defined path, allowing the contained weapon to slide back a 

short distance . . . shifting the trigger away from the shooter’s trigger finger.” Appellee’s Br. at 

18 (citing 83 Fed. Reg. at 66,532 (Dec. 26, 2018)). “This separation allows the firing mechanism 

to reset.” Id. The shooter must also “maintain constant forward pressure on the weapon’s barrelshroud or fore-grip . . . causing the trigger to ‘bump’ the shooter’s stationary finger and fire 

another bullet.” Id. This explanation reveals a couple of reasons why a bump stock does not 

transform a rifle into a machinegun.

First, a bump stock does not create all of the above-described effects itself—one still 

needs to maintain constant forward pressure on the weapon’s barrel-shroud or fore-grip. Thus, a 

semiautomatic rifle does not shoot automatically and thereby become a machinegun, simply by 

having a bump stock. When the National Firearms Act was enacted, the word “automatically” 

meant “[h]aving a self-acting or self-regulating mechanism that performs a required act at a 
No. 20-6380 Hardin v. ATF, et al. Page 12

predetermined point in an operation[.]” Webster’s New International Dictionary (2d ed. 1934). 

While the bump stock might be a self-acting mechanism to allow the rifle to slide back, it is not a 

self-acting mechanism to maintain the forward pressure. Without that added technique, the 

bump stock would not increase the rate of fire, and the rifle therefore cannot be considered a 

machinegun because of the addition of a bump stock.

Second, the “single function of a trigger” on a rifle with a bump stock engages the 

internal firing mechanism to shoot only one shot, in contrast with the definition of a machinegun 

“automatically [shooting] more than one shot.” 26 U.S.C. § 5845(b). Once a trigger is pulled, 

the hammer strikes the firing pin to shoot one bullet. See Cargill v. Garland, 57 F.4th at 452. 

Then, the hammer is thrusted backward by the bolt into the disconnector. Id. The hammer will 

stay in the disconnector until the trigger is reset to its original position. Id. This means that the 

“single function of the trigger” will only release one bullet because the trigger must reset each 

time before it can engage the hammer to strike the firing pin to release another bullet. In 

contrast, an automatic gun will continue to reset the hammer and release the hammer without the 

trigger resetting to its original position, so a “single function of a trigger” can lead to the 

shooting of multiple shots. See id. A bump stock does nothing to impact the internal mechanics 

of a rifle to circumvent the need for the trigger to reset between every shot, so a bump-stockequipped rifle is still capable of shooting only one shot with each function of the trigger.

II.

The ATF attempts to replace “single function of the trigger,” as the definition reads in the 

National Firearms Act, with “single pull of the trigger.” 83 Fed. Reg. at 66,518. This new 

agency-created definition, announced after high-profile statements from President Trump and 

others in response to the Las Vegas shooting,1is an about-face from the ATF’s original 

interpretation of the statute. ATF Rule 2006-2 at 2; 27 C.F.R. §§ 478.11 (2014), 479.11 (2016). 

1Presidential Memorandum on the Application of the Definition of Machinegun to “Bump Fire” Stocks and 

Other Similar Devices, President Donald Trump (Feb. 20, 2018) (on file with the White House Archives); Lindsey 

McPherson, Pelosi Optimistic About Gun Control Bill Short of Assault Weapons Ban, ROLL CALL, Mar. 1, 2018; 

Statement on Regulation to Ban Bump Stocks, Senator Dianne Feinstein (Dec. 18, 2018); Department of Justice 

Announces Bump-Stock-Type Devices Final Rule Press Release, Department of Justice Office of Public Affairs 

(Dec. 18, 2018). 
No. 20-6380 Hardin v. ATF, et al. Page 13

There were no changes in the relevant facts or law that led to the ATF making a 180-degree 

change of statutory interpretation to ban what once was legal. There was only a profound change 

in political pressure. 

Even if the ATF had adopted its current view from the get-go, that interpretation fits 

poorly with the statutory text. The ATF substitutes “pull” for “function” to argue that there is a 

single “pull” from the shooter’s perspective. But the statutory definition defines “function” not 

with reference to the shooter but to the firearm, given the use of the word “trigger,” which is a 

mechanical feature. From the firearm’s mechanical perspective, the trigger must fully reset and 

be “pulled” every single time another shot is fired, so substitution of the ATF’s new word, “pull” 

for “function,” does not make a bump-stock rifle a machinegun. Even with the bump stock, the 

trigger of the rifle still must be pulled—that is, the trigger finger must move against the trigger 

while the shooter maintains forward pressure on the weapon’s barrel-shroud or fore-grip—for 

each shot the weapon fires. See Gun Owners of Am., Inc., 19 F.4th at 913–14, 926–27 (Murphy, 

J., dissenting). To be sure, the bump stock allows for multiple shots to occur more rapidly, but 

that consequence does not change the dispositive fact that each pull of the trigger fires only one 

shot. Because a single function of the trigger using a bump stock cannot fire more than one 

bullet, a bump-stock rifle is not a machinegun.

I therefore concur in reversing the district court judgment because the best reading of the 

statute is that bump stocks are legal. The statutory text confirms that the ATF correctly 

interpreted the statute the first time. It is the job of Congress, not the ATF, to decide whether the 

law should change in this area.