Damien Guedes v. ATF

United States Court of Appeals
FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued March 8, 2022 Decided August 9, 2022

No. 21-5045

DAMIEN GUEDES, ET AL.,
APPELLANTS

FIREARMS POLICY COALITION, INC.,
APPELLEE

v.

BUREAU OF ALCOHOL, TOBACCO, FIREARMS AND EXPLOSIVES,
ET AL.,
APPELLEES

Appeal from the United States District Court
for the District of Columbia
(No. 1:18-cv-02988)

Erik S. Jaffe argued the cause for appellants. With him on
the briefs were Joshua G. Prince, Adam Kraut, and Joshua J.
Prince.

John Cutonilli, pro se, was on the brief for amicus curiae
John Cutonilli in support of appellants.
 2
Mark B. Stern, Attorney, U.S. Department of Justice,
argued the cause for appellees. With him on the brief were
Brian M. Boynton, Acting Assistant Attorney General, and
Michael S. Raab, Abby C. Wright, Brad Hinshelwood, and Kyle
T. Edwards, Attorneys.

Ian Simmons, Jonathan Lowy, and Eric Tirschwell were
on the brief for amici curiae Giffords Law Center to Prevent
Gun Violence, and Brady and Everytown for Gun Safety in
support of appellees.

Before: SRINIVASAN, Chief Judge, WILKINS, Circuit
Judge, and EDWARDS, Senior Circuit Judge.

Opinion for the court filed by Circuit Judge WILKINS.

WILKINS, Circuit Judge: Is a bump stock device a
“machine gun” within the meaning of federal law? We are
tasked with answering that question definitively. Following
the 2017 mass shooting in Las Vegas in which 58 people were
killed and approximately 500 were wounded—the deadliest in
modern American history—the Bureau of Alcohol, Tobacco,
Firearms, and Explosives (“ATF” or the “Bureau”)
promulgated a rule classifying “bump stocks” as machine
guns.1 A bump stock, like those used by the Las Vegas shooter,
replaces a rifle’s stationary stock with a sliding stock. It
thereby enables the weapon to slide back and forth against the
shooter’s shoulder, “bumping” the shooter’s trigger finger
repeatedly and rapidly firing the weapon. The Bureau’s new
rule instructed individuals with bump stocks to either destroy

1
We follow the previous panel’s example and use the two-word
spelling of “machine gun” except when directly quoting sources.
Guedes v. ATF, 920 F.3d 1, 6 n.1 (D.C. Cir. 2019).
 3
them, abandon them at the nearest ATF facility, or face
criminal penalties.

The Bureau interpreted “machine gun,” as defined in the
National Firearms Act and Gun Control Act, to extend to bump
stocks. Plaintiffs initially moved for a preliminary injunction
to stop the rule from taking effect, which the District Court
denied, and a panel of this Court affirmed. At the merits stage,
the District Court again rejected Plaintiffs’ challenges to the
rule under the Chevron framework. See Chevron, U.S.A., Inc.
v. Natural Resources Defense Council, Inc., 467 U.S. 837
(1984). The central question on appeal is whether the Bureau
had the statutory authority to interpret “machine gun” to
include bump stocks. Employing the traditional tools of
statutory interpretation, we find that the disputed rule is
consistent with the best interpretation of “machine gun” under
the governing statutes. We therefore affirm.

I.

A.

Congress enacted the National Firearms Act in 1934 to
regulate the sale of particular firearms, including machine
guns. Initially, the Act defined a “machine gun” as “any
weapon which shoots, or is designed to shoot, automatically or
semiautomatically, more than one shot, without manual
reloading, by a single function of the trigger.” Pub. L. No. 73-
474, § 1(b), 48 Stat. 1236, 1236 (1934). In 1968, Congress
removed “or semiautomatically” and expanded the definition
to include:

the frame or receiver of any such weapon, any
combination of parts designed and intended for use in
converting a weapon into a machinegun, and any
 4
combination of parts from which a machinegun can be
assembled.

Pub. L. 90-618, 82 Stat. 1213, 1231 (1968). Congress charged
the Attorney General with enforcement of the National
Firearms Act, who in turn delegated enforcement authority to
the Bureau. 26 U.S.C. § 7801(a); 28 C.F.R. § 0.130(a).

With the Gun Control Act of 1968, Congress incorporated
the National Firearms Act’s definition of “machinegun” and
strengthened its prohibitions on firearm sales and licensing. 18
U.S.C. § 922(a)(4). As amended by the Firearm Owners’
Protection Act of 1986, the Gun Control Act prohibits the
transfer of or possession of machine guns, excluding those
authorized to possess such weapons by the state or federal
government or those who possessed them before the law took
effect. 18 U.S.C. § 922(o). The Gun Control Act’s
enforcement scheme is identical to that of the National
Firearms Act. Congress empowered the Attorney General to
“prescribe only such rules and regulations as are necessary to
carry out the provisions of this chapter,” who delegated this
authority, in turn, to the Bureau. Id. § 926(a); 28 C.F.R.
§ 0.130(a)(6).

In 2006, the Bureau determined that certain bump stock
devices—ones that harnessed energy from an internal spring’s
recoil, like an Akins Accelerator—qualified as machine guns
under both Acts. See ATF Rul. 2006-2. Between 2008 and
2017, however, the Bureau issued ten letter rulings in which it
concluded that devices relying on both the recoil energy and
the shooter’s constant forward pressure were not machine guns.
These weapons fired multiple shots with a “single pull of the
trigger,” but in the Bureau’s view did not operate
 5
“automatically,” though the Bureau did not engage with the
meaning of the term. Id. at 66,518.2

In the aftermath of the Las Vegas shooting, then-President
Trump and Congress urged the Bureau to revisit its position on
bump stocks. Department of Justice Announces Bump-Stock-
Type Devices Final Rule, DEP’T OF JUST. (Dec. 18, 2018),
https://www.justice.gov/opa/pr/department-justice-announces-
bump-stock-typedevices-final-rule, J.A. 21–22. Following a
notice of proposed rulemaking, see Bump-Stock-Type Devices,
83 Fed. Reg. 13,442 (Mar. 29, 2018), the Bureau issued a final
rule reversing its earlier position that only bump stocks with
internal springs qualified as machine guns under the National
Firearms Act and Gun Control Act. Bump-Stock-Type Devices,
83 Fed. Reg. 66,514, 66,514–15 (Dec. 26, 2018) (“Bump Stock
Rule” or “Rule”). Under the Rule, “bump-stock-type devices
are ‘machineguns’ as defined by the National Firearms Act and
Gun Control Act because such devices allow a shooter of a
semiautomatic firearm to initiate a continuous firing cycle with
a single pull of the trigger.” Id. at 66,515. These devices,
whether operated by an internal spring or manual pressure,
“convert an otherwise semiautomatic firearm into a
machinegun.” Id.

The Rule defined “single function of the trigger” as a
“‘single pull of the trigger’ and analogous motions” and
“automatically” as “the result of a self-acting or self-regulating
mechanism that allows the firing of multiple rounds through a
single pull of the trigger.” Id. Individuals currently in
possession of bump stocks were directed to either destroy them

2
These devices included one from the manufacturer of at least one
of the bump stock devices used in the Las Vegas shooting. Id. at
66,516.
 6
or abandon them at an ATF facility prior to the rule taking
effect on March 26, 2019. Id. at 66,514, 66,515.

B.

In December 2018, pursuant to the Bureau’s notice of final
rulemaking, Plaintiffs sought a preliminary injunction to
prevent the rule from taking effect. The District Court denied
that request, finding the Bureau’s interpretation of the relevant
statutory terms—“single function of the trigger” and
“automatically”—reasonable under Chevron. Guedes v. ATF,
356 F. Supp. 3d 109 (D.D.C. 2019) (“Guedes I”).

We affirmed the District Court’s decision on the same
basis. Guedes v. ATF, 920 F.3d 1, 6 (D.C. Cir. 2019) (per
curiam) (“Guedes II”). In our view, the Chevron framework
applied, notwithstanding Plaintiffs’ objections, because the
rule was legislative in character; the government could not
waive Chevron deference; and Chevron applies in equal force
to provisions with criminal penalties. Id. at 17–28. Because
we found “single function of the trigger” and “automatically”
ambiguous under the National Firearms Act and Gun Control
Act and the agency’s interpretations reasonable, we ruled in the
Bureau’s favor.

The Supreme Court denied Plaintiffs’ petition for
certiorari. Guedes v. ATF, 140 S. Ct. 789 (2020) (Mem.). In a
separate statement, Justice Gorsuch articulated his view that
Chevron did not apply because of the government’s express
waiver of the doctrine and the statute’s criminal penalties. Id.
at 790. He nevertheless concurred in the petition’s denial,
finding that the government’s position could be substantiated
at the merits stage and noting that other courts of appeals were
currently considering challenges to the Rule. Id. at 791.
 7
Now before us is the District Court’s grant of the
government’s motion for summary judgment and denial of
Plaintiffs’ cross-motion for summary judgment. Guedes v.
ATF, 520 F. Supp. 3d 51, 58 (D.D.C. 2021) (“Guedes III”). For
the same reasons discussed in Guedes I and II, the District
Court found the Bureau reasonably construed the statute under
Chevron and rejected Plaintiffs’ challenges on the merits. Id.
at 65.

II.

We have jurisdiction over this appeal under 28 U.S.C. §
1291, and we review a grant or dismissal of a motion for
summary judgment de novo. Baylor v. Mitchell Rubenstein &
Assocs., P.C., 857 F.3d 939, 944 (D.C. Cir. 2017).

III.

A.

The government urges us to decide this appeal based on
the law of the case doctrine, which instructs that “the same
issue presented a second time in the same case in the same
court should lead to the same result.” LaShawn A. v. Barry, 87
F.3d 1389, 1393 (D.C. Cir. 1996). The doctrine is a
discretionary prudential doctrine, not a jurisdictional bar, and
we decline to apply it here. Crocker v. Piedmont Aviation, Inc.,
49 F.3d 735, 739–40 (D.C. Cir. 1995). This is not a situation
in which we are reaching a different result on the same legal
issue in the same case, which could require showing
“extraordinary circumstances.” Sherley v. Sebelius, 689 F.3d
776, 781 (D.C. Cir. 2012) (quoting LaShawn A., 87 F.3d at
1393). Rather, we ultimately reach the “same result” as the
Guedes II panel, id., in that we likewise sustain the Bump Stock
Rule.
 8

If we were reaching a different result, we would assess our
discretionary decision to do so under “the preliminary
injunction exception to the law-of-the-case doctrine.” Sherley,
689 F.3d at 781. We need not fit within that exception, though,
in circumstances in which we reach the same result. To be sure,
we reach that result via a different path. But we are unaware
of any decision saying that the pursuit of a different path—as
opposed to the reaching of a different result—requires fitting
within an exception to the law-of-the-case doctrine or a
showing of extraordinary circumstances, especially when we
have no need here to revisit the reasoning of the Guedes II
panel. And we explain next why we opt to sustain the validity
of the Bump Stock Rule in a different way than did that panel.

B.

The threshold question is whether to treat this case as a
matter of pure statutory interpretation or to apply the Chevron
framework. Both parties advocate for the former. Plaintiffs
argue that Chevron does not apply for a multitude of reasons:
the rule is interpretive in nature; the government waived
Chevron deference; the Court may not apply Chevron to a
statute with criminal penalties; and the rule of lenity must
supersede Chevron in the criminal context. The Bureau also
characterizes the Rule as interpretive, and it likewise urges us
to analyze the Rule under a statutory interpretation framework.

The Guedes II panel employed the Chevron framework—
just as the District Court had done—in denying the motion for
preliminary injunction. The panel concluded that the Bump
Stock Rule was a legislative rule; the Bureau explicitly relied
on Chevron in crafting it; the government cannot recharacterize
a rule as legislative or interpretative during litigation; and the
government cannot waive Chevron. 920 F.3d at 18, 21–23.
 9

Ultimately, we need not wrestle with the Chevron
framework here. Rather, the parties have asked us to dispense
with the Chevron framework, and in this circumstance, we
think it is appropriate to do so. See Am. Hosp. Ass’n v. Becerra,
142 S. Ct. 1896 (2022) (rejecting agency’s interpretation “after
employing traditional tools of statutory interpretation,” rather
than inquiring into the interpretation’s reasonableness under
Chevron). Using a statutory interpretation lens, we decide that
the Bureau offered the best construction of the statute without
wading into the subsidiary questions that the Chevron analysis
poses.

This approach also comports with how the Bureau
engaged in the rulemaking exercise. The Bureau repeatedly
described what it was doing as seeking to arrive at the “best
interpretation” of the statutory text, and it relied principally on
that reasoning during the rulemaking. Bump Stock Rule, 83
Fed. Reg. at 66,514, 66,517, 66,518, 66,521. This is also the
Bureau’s principal position on appeal. Appellee Br. 28. While
the Bureau contended that it would reach the same result using
a Chevron framework, that argument served as its fallback
position. 83 Fed. Reg. at 66,527 (explaining that “this rule’s
interpretations of ‘automatically’ and ‘single function of the
trigger’ in the statutory definition of ‘machinegun’ accord with
the plain meaning of those terms,” but that “even if those terms
are ambiguous, this rule rests on a reasonable construction of
them”). This jurisprudential approach thus allows us to address
the issues as the parties have principally framed them for
resolution. If we are able to uphold the Bureau’s definition
based on its primary line of argument, there is no reason to
reach its secondary one. See HollyFrontier Cheyenne Ref.,
LLC v. Renewable Fuels Ass’n, 141 S. Ct. 2172, 2180 (2021)
(declining to consider whether Chevron deference was due
where government did not invoke it).
 10

Finally, there is no need to decide what deference, if any,
a regulation should receive where we can conclude that the
agency’s interpretation of the statute is the best one. Our
decision to forgo engaging with questions of Chevron’s
applicability is consistent with how courts have approached
agency interpretation issues in the past. As the Supreme Court
explained in Edelman v. Lynchburg College, “there is no need
to resolve any question of deference,” where the agency
regulation is “not only a reasonable one, but the position we
would adopt even if there was no formal rule and we were
interpreting the statute from scratch.” 535 U.S. 106, 114
(2002). That is not to say that the agency’s rule must be the
only “permissible” interpretation of the statute, but only that it
must be the best construction. Id. at 114 & n.8. See also
Washington Reg’l Medicorp v. Burwell, 813 F.3d 357, 362
(D.C. Cir. 2015) (finding no need to engage in deference
analysis where agency’s interpretation is both reasonable and
the best interpretation of the statute); Am. Hosp. Ass’n v.
Becerra, 142 S. Ct. at 1896 (employing “traditional tools of
statutory interpretation” to analyze an agency rule, without
resort to Chevron or any other form of deference to the agency);
Becerra v. Empire Health Found., 142 S. Ct. 2354, 2368 (2022)
(same).

So too here, in relying on the ordinary tools of statutory
interpretation—“text, structure, purpose, and legislative
history,” see Pharm. Rsch. & Mfrs. of Am. v. Thompson, 251
F.3d 219, 224 (D.C. Cir. 2001)—we find that the Bureau has
provided the best reading of the statute and that the statutory
definition of machine gun as articulated in 26 U.S.C. § 5845(b)
extends to bump stocks.
 11
(i)

Recall the National Firearms Act and Gun Control Act’s
definition of “machinegun”:

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). Whether this definition encompasses
bump stocks depends on how we interpret two of its interior
phrases—“single function of the trigger” and
“automatically”—and how those phrases relate to one another.

Starting with “single function of the trigger,” the Bureau
interprets it as a “‘single pull of the trigger’ and analogous
motions.” Bump Stock Rule, 83 Fed. Reg. at 66,515. The
phrase “analogous motions” includes “other methods of
initiating an automatic firing sequence that do not require a
pull,” like a push of a button or voice command. 83 Fed. Reg.
at 66,515, 66,534–35. The Bureau’s interpretation of “single
function of the trigger” thus both defines a “function” of the
trigger as a “pull” of the trigger and clarifies that a “pull” of the
trigger is a shooter’s volitional action that initiates an automatic
firing sequence.

The Bureau offers the best reading of the statutory phrase
in light of the plain language and purpose of the statute,
 12
particularly as compared to Plaintiffs’ unworkable definition.
To begin, the Bureau recognized that it was not interpreting
“single function of the trigger” on a blank slate. In Staples v.
United States, 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,” in
contrast to one “that fires only one shot with each pull of the
trigger.” 511 U.S. 600, 602 n.1 (1994) (emphasis added).
Further, in Akins v. United States, 312 Fed. App’x 197, 200
(11th Cir. 2009) (per curiam), 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 Bureau explicitly drew upon both interpretations
in crafting its own. See Bump Stock Rule, 83 Fed. Reg. at
66,518, 66,527 (quoting Staples, 511 U.S. at 602 n.1; Akins,
312 Fed. App’x at 200). See also United States v. Camp, 343
F.3d 743, 745 (5th Cir. 2003) (using “pull” and “function”
synonymously in classifying weapon as a machine gun).

Such an interpretation is also consonant with the ordinary
meaning of “function” at the time of the statute’s enactment.
Asgrow Seed Co. v. Winterboer, 513 U.S. 179, 187 (1995)
(“When terms used in a statute are undefined, we give them
their ordinary meaning.”).3 In 1934, “function” was defined as

3
Plaintiffs rely on the 1968 dictionary definitions of these terms,
arguing that Congress “narrowed” the definition of machine gun that
year in enacting the Gun Control Act. Appellants’ Opening Br. 23,
27. But “unless otherwise defined, words will be interpreted as
taking their ordinary, contemporary, common meaning at the time
Congress enacted the statute.” Amoco Prod. Co. v. S. Ute Indian
Tribe, 526 U.S. 865, 874–75 (1999) (internal quotation marks and
citation omitted). See also ANTONIN SCALIA & BRYAN A. GARNER,
READING LAW: THE INTERPRETATION OF LEGAL TEXTS 78 (2012)
(“Words must be given the meaning they had when the text was
 13
“to perform, execute” or an “activity; doing; performance.”
Function, WEBSTER’S NEW INTERNATIONAL DICTIONARY (2d
ed. 1934). With respect to the statute, the shooter’s pull is the
single “activity” or “performance” of the trigger that causes the
gun to shoot automatically more than one shot. (Where a
different activity causes the trigger to shoot, like the flip of a
switch, the regulation accounts for it through the inclusion of
“and analogous motions.”).

Indeed, as early as Congress began discussing restrictions
on machine guns through the National Firearms Act, a “single
function of the trigger” was understood to mean a “single pull.”
Congress initially proposed a definition of “machine gun”
based on a weapon’s capability to fire multiple shots,
specifically a firearm that could automatically or
semiautomatically shoot “twelve or more shots without
reloading.” See National Firearms Act: Hearings Before the
Comm. on Ways and Means, H.R., on H.R. 9066, 73d Cong. 1
(1934). Testifying before Congress, President of the National
Rifle Association Karl T. Frederick advocated for an
alternative definition that omitted the number of shots required
and incorporated the “single function of the trigger” language.
Id. at 40. Mr. Frederick further explained that “[t]he
distinguishing feature of a machine gun is that by a single pull
of the trigger the gun continues to fire as long as there is any
ammunition in the belt or in the magazine.” Id.4 Roughly one

adopted.”). Given that Congress enacted the National Firearms Act
in 1934, we look to dictionary definitions at that time.
4
Frederick also testified that an automatic Colt pistol would not be a
machine gun under his proposed definition because it “require[d] a
separate pull of the trigger for every shot fired.” Id. at 41. (The name
of this weapon is deceptive, given that the ATF classified an
automatic Colt Pistol as a semiautomatic firearm. See ATF, NEWS
MEDIA GUIDE TO FIREARMS 5–6 (1978)). Frederick’s testimony on
 14
month later, Congress adopted Frederick’s definition word for
word. Id. at 83. See also H.R. Rep. No. 73-1780, at 2 (1934)
(noting the bill’s “usual definition of machine gun as a weapon
designed to shoot more than one shot without reloading and by
a single pull of the trigger”). Reading “single function” to
mean a “single pull” thus reflects the term’s contemporaneous
understanding.

This definition also aligns with Congress’s purpose in
enacting federal legislation on machine guns to “[s]trictly
regulate the manufacture, sale, transfer and possession of
destructive devices” and to “combat the spiralling increase in
serious crime in the United States.” S. Rep. No. 90-1097, at
2,290 (1968); see also Huddleston v. United States, 415 U.S.
814, 824 (1974) (“principal purpose” of the Gun Control Act
was to reduce crime) (quoting id. at 2,113–14). Congress’s
concern for the danger posed by machine guns centered on their
destructive potential and exacerbation of serious crime. Bump
stocks present a heightened capacity for lethality as well; they
are estimated to fire between 400 and 800 bullets per minute,
as compared to a semiautomatic weapon’s 180 bullets per
minute. Amicus Br. for Appellee at 19–20. It is therefore
consistent with congressional purpose to define “single
function” with a focus on the weapon’s ease of use.

Turning to “automatically,” the statutory text similarly
favors the Bureau’s definition. The Bureau defines
“automatically” as “the result of a self-acting or self-regulating
mechanism that allows the firings of multiple rounds.” Bump
Stock Rule, 83 Fed. Reg. at 66,554. This definition pulls

this score supports the Bureau’s interpretation that an automatic gun
requires a single pull to set off a sequence of multiple shots, whereas
a semiautomatic gun requires a distinct pull for each shot. Appellee
Br. 47–48.
 15
directly from dictionaries of the 1930s, which defined
“automatic” as “having a self-acting or self-regulating
mechanism that performs a required act at a predetermined
point in an operation;—said esp. of machinery or devices
which perform work formerly or usually done by hand.” Bump
Stock Rule, 83 Fed. Reg. at 66,519; Automatic, WEBSTER’S
NEW INTERNATIONAL DICTIONARY (2d ed. 1934). The term
speaks of a mechanized process that requires less human
exertion than an activity “usually done by hand.”

The Bureau’s prior interpretation of “automatically”
focused more on the “self-acting” portion of the definition. 83
Fed. Reg. at 66,517–18. It previously concluded that a device
must contain a spring or similar self-acting mechanism in order
to operate “automatically”—therefore, bump stocks did not
operate “automatically” because they required some manual
input. Id. In the current rulemaking, the Bureau correctly
recognized not only that “self-acting” can admit of some
human input, but also that the word “automatically”
encompasses devices that are “self-regulating.” Id. at 66,519.

This definition has found approval in past judicial
interpretations. In United States v. Olofson, the Seventh Circuit
concluded that under the National Firearms Act, “the adverb
‘automatically’ . . . delineates how the discharge of multiple
rounds from a weapon occurs: as the result of a self-acting
mechanism. That mechanism is one that is set in motion by a
single function of the trigger and is accomplished without
manual reloading.” 563 F.3d 652, 658 (7th Cir. 2009).

Statutory context also helps guide our interpretation here,
given that “automatic” cannot be read in isolation. The statute
defines a machine gun as a weapon that shoots “automatically
more than one shot, without manual reloading, by a single
function of the trigger.” 26 U.S.C. § 5845(b) (emphasis
 16
added). Equally important is the term “by,” defined as
“through the means of; in consequence of;—indicating that
which is instrumental; as, to take by force; to win regard by
showing kindness; to teach by example.” By, WEBSTER’S NEW
INTERNATIONAL DICTIONARY (2d ed. 1934). As used in the
statute, a machine gun is a weapon that automatically shoots
more than one shot “through the means of” or “in consequence
of” a single function of the trigger.

Rather than limiting the term “automatically,” the phrase
“by a single function” clarifies it. With the use of “by,” “single
function” is best understood as the antecedent to
“automatically”—the initiating human action that sets off a
self-regulating sequence of events. See United States v. Evans,
978 F.2d 1112, 1113 n.2 (9th Cir. 1992) (“‘by a single function
of the trigger’ describes the action that enables the weapon to
‘shoot . . . automatically . . . without manual reloading,’ not the
trigger mechanism.”). The statute does not suggest that human
involvement is confined to the “predetermined point” of the
operation. Instead, “rather than reading the phrase ‘by a single
function of the trigger’ to mean ‘by only a single function of
the trigger,’ the phrase can naturally be read to establish only
the preconditions for setting off the ‘automatic’ mechanism,
without foreclosing some further degree of manual input.”
Guedes II, 920 F.3d at 31.

In sum, under the National Firearms Act and Gun Control
Act, a “single function” of the trigger is best understood as a
“single pull of the trigger” and “analogous motions,” while
automatically is best understood to mean a “result of a self-
acting or self-regulating mechanism.” 83 Fed. Reg. at 66,514.
Taken together, these interpretations provide the best definition
of a machine gun.
 17
(ii)

The best definition of machine gun settled, we turn to
whether a bump stock fits within it. In terms of how a bump
stock operates, the District Court found as follows: “A bump
stock replaces a semiautomatic rifle’s standard stock—the part
of the rifle that rests against the shooter’s shoulder—and
enables the shooter to achieve a faster firing rate. To use a
bump stock, the shooter must maintain forward pressure on the
barrel and, at the same time, pull the trigger and maintain
rearward pressure on the trigger. Once the shooter pulls the
trigger, a bump stock harnesses and directs the firearm’s recoil
energy, thereby forcing the firearm to shift back and forth, each
time ‘bumping’ the shooter’s stationary trigger finger. In this
way, the shooter is able to reengage the trigger without
additional pulls of the trigger.” Guedes III, 520 F. Supp. 3d at
58, J.A. 43–44. Plaintiffs conceded that they were not
challenging any of the District Court’s factual findings. See
Appellants’ Opening Br. 20 (“there is no confusion or dispute
whatsoever regarding how a bump stock physically works”);
Oral Arg. Tr. at 83–84 (answering “no” to the question of
whether Appellants contended that the “District Court
erroneously found a fact to be undisputed that was actually
disputed”). Based on these facts, a bump stock is a machine
gun under the best interpretation of the statute.

It bears noting that these factual findings correspond with
the Bureau’s statement of undisputed facts submitted in support
of a motion for summary judgment, which cited evidence in the
record in support of each statement. See Dkt. 61-3 ¶¶ 70–73
(“[u]sing a bump stock as designed and intended, a shooter
does not need to pull the trigger more than once to produce
more than one shot”). Plaintiffs did not properly dispute these
facts, because their opposition failed to cite any evidence, as
required by the federal and local rules. See Dkt. 63-1 ¶¶ 70–
 18
73; Fed. R. Civ. P. 56(c)(1)(A); Local Rule 7(h)(1).5 “While
the local rules provide the mechanics, the Federal Rules of
Civil Procedure explicitly require a party opposing summary
judgment to support an assertion that a fact is genuinely
disputed with materials in the record.” Oviedo v. Washington
Metro. Area Transit Auth., 948 F.3d 386, 396 (D.C. Cir. 2020).
See also Bush v. D.C., 595 F.3d 384, 387 (D.C. Cir 2010);
Jackson v. Finnegan, Henderson, Farabow, Garrett & Dunner,
101 F.3d 145, 150–51 (D.C. Cir. 1996).

Analyzing the District Court’s factual findings under the
Bump Stock Rule, we conclude that they are consistent with
the best interpretation of the statute. First, as the District Court
explained, a shooter operates a bump stock by a single pull,
eliminating the need for additional pulls. Guedes III, 520
F. Supp. 3d at 58, J.A. 44. The shooter pulls the trigger once
and his finger rests against the extension ledge, or the edge of
the bump stock device. See J.A. 35.6 After the first pull of the
trigger, the stock moves repeatedly back-and-forth, causing the
trigger to “bump” against the stationary finger. Thus, only a
single “function” or “pull” of the trigger by the shooter
activates the multiple-shot sequence; no further pulls are
needed. Put differently, using a bump stock, a single pull of
the trigger propels the trigger against the stationary finger and

5
For example, in response to the Bureau’s description of the trigger
pull initiating a firing sequence, Plaintiffs responded, “In dispute as
to the phrasing of multiple portions of the statement; which are
attempts to draw legal conclusions, not accurately describe facts.”
Dkt. 63-1 ¶ 71.
6
Plaintiffs entered a video into the record demonstrating how a bump
stock operates. J.A. 35 (citing Patton Media & Consulting, LLC,
Bump Stock Analytical Video FPC/FICG, YOUTUBE (June 14,
2018), https://youtu.be/1OyK2RdO63U). The attached appendix
includes still photographs taken from that video, depicting the
function of the trigger.
 19
causes the subsequent shots through the force of recoil from
firing the first bullet. Following the initial pull of the trigger,
if nothing changes (i.e., the shooter maintains forward pressure
on the barrel), the firearm will continue to fire additional shots
continuously. As found by the District Court, the shooter is
“able to reengage the trigger without additional pulls of the
trigger.” 520 F. Supp. 3d at 58, J.A. 44.

Second, a bump stock functions automatically because it
is self-regulating. The bump stock “harnesses and directs the
firearm’s recoil energy” along a linear path, “thereby forcing
the firearm to shift back and forth.” Guedes III, 520 F. Supp.
3d at 58, J.A. 43–44. That process will not conclude until the
shooter releases forward pressure on the barrel, the weapon
runs out of ammunition, or it malfunctions. In other words, a
bump stock regulates the weapon’s back-and-forth movement
after a predetermined point in an operation—the shooter’s pull
of the trigger—and remains self-regulating as long as the
shooter maintains pressure on the barrel.

Looking to the specific bump stock devices at issue, even
the manufacturer’s description admits of this interpretation of
“automatic.” Plaintiff Damien Guedes purchased his bump
stock device from Bump Fire Systems, while Plaintiff Shane
Roden purchased a Slide Fire bump stock device. See Am.
Compl. at 19–20, Guedes I (No.18-cv-02988). In an
explanation of firing with a bump stock, the manufacturer
Bump Fire Systems described it as a legal method of “full-auto
firing.” Administrative Record 840. According to the
description, the shooter operates the bump stock “by gripping
the fore-end of the barrel and pulling it forward,” allowing him
“to recreate the feeling of automatic firing.” Id. This
description confirms what the Bureau sets forth: a bump stock
enables a shooter to engage in automatic firing by pulling the
trigger and maintaining pressure on the stock.
 20

This interpretation of “automatically” also comports with
how the United States Patent and Trademark Office
(“USPTO”) interprets the term with respect to firearms.
During the rulemaking process, the Bureau observed that Slide
Fire, the manufacturer of the bump stocks used in the Las
Vegas shooting, “has obtained multiple patents for its designs,
and has rigorously enforced the patents to prevent competitors
from infringing them.” 83 Fed. Reg. at 13,443; see also 83
Fed. Reg. at 66,538, 66,545 (discussing patents); J.A. 32, Dkt.
61-1 at 16 (discussing patent application); Dkt. 61-3 ¶ 42
(referring to patents); Administrative Record 382–90 (patent
application); id. at 834 (referring to patents). The USPTO has
classified three different Slide Fire bump stock patents as
primarily within the subclass 89/140,7 which is used for
weapons that are “[c]onvertible to full automatic,” meaning
“[g]uns wherein the firing device is selectively operable either
full-automatic or semi-automatic.” Class 89 Ordnance,
Classification Resources, USPTO, https://bit.ly/3c92Dyd.8
The USPTO further explains that “[t]he terms ‘full-automatic’
or ‘automatic’ are applied to firing devices which effect
continuous fire as long as the trigger is retracted and
ammunition is supplied to the gun.” Id. While not dispositive,
it is nonetheless significant that the USPTO classifies the bump
stock as a device that enables a semiautomatic weapon to

7
U.S. Patent No. 8,356,542, at [52]; U.S. Patent No. 8,176,835, at
[52]; U.S. Patent No. 8,127,658, at [52].
8
In the USPTO classification system, “[s]ubclasses delineate
processes, structural features, and functional features of the subject
matter encompassed within the scope of a class.” Amgen Inc. v.
F. Hoffman-La Roche, Ltd., 580 F.3d 1340, 1347 n.1 (Fed. Cir.
2009).
 21
operate in a manner functionally equivalent to that of a fully
automatic weapon.9

Accordingly, under the best interpretation of the statute, a
bump stock is a self-regulating mechanism that allows a
shooter to shoot more than one shot through a single pull of the
trigger. As such, it is a machine gun under the National
Firearms Act and Gun Control Act.

(iii)

Unlike the Bureau, Plaintiffs have failed to show that their
“machine gun” definition is workable. See United States v.
California, 381 U.S. 139, 165 (1965) (“we best fill our
responsibility of giving content to the words which Congress
employed by adopting the best and most workable definitions
available”). With regard to “single function of the trigger,”
Plaintiffs argue for a trigger-focused, rather than a shooter-
focused, interpretation. In their view, the statutory language
refers to the mechanical action of the trigger itself. See
Appellants’ Opening Br. 23–24 (“‘function’ thus most
reasonably refers to the mechanical action of the trigger” and
“the function of the trigger is complete when the hammer is
released, and a shot is fired”). Drawing upon the Sixth
Circuit’s now-overturned opinion, they contend that this phrase
“necessarily refers to the trigger and not to the shooter or the
shooter’s act of pulling.” Appellants’ Opening Br. 23 (quoting
Gun Owners of America, Inc. v. Garland, 992 F.3d 446, 471

9
What’s more, all three patents describe a key feature of the bump
stock as directing the recoil force along a “constrained linear path,”
see ‘542 Patent col. 3, l. 23; ‘835 Patent col. 7, l. 51; ‘658 Patent col.
3, l. 49–50, which is the “self-regulating” (i.e. automatic) feature that
enables the recoil of the weapon to propel the trigger repeatedly into
the stationary finger, resulting in the continuous firing of the weapon.
See supra at 19.
 22
(6th Cir. 2021), vacated, 19 F.4th 890 (6th Cir. 2021) (en
banc)). Thus, “[a]ny subsequent bump, pull, or other
interaction between the shooter’s finger and the
trigger . . . causes a second or subsequent function of the
trigger, not a continuation of the initial completed function.”
Id. at 24. Because a semiautomatic gun outfitted with a bump
stock releases the hammer for each discharge, they assert that
it does not fire more than one round via a single function of the
trigger.

Yet, when asked at oral argument whether a hypothetical
invention—a mechanical hand with a fast, continuously
moving trigger finger that could be attached to a semiautomatic
gun and operated by a push of a button—qualified as a machine
gun, Plaintiffs answered in the affirmative. Oral Arg. Tr. at
81–83; see also id. at 56 for earlier discussion. According to
Plaintiffs, we could redefine the trigger in this scenario to the
button being pressed, rather than the internal trigger
mechanism. But this reasoning diverges from Plaintiffs’
definition of “single function of the trigger” as a mechanistic
act of the conventional firearm trigger itself. There are no two
ways about it: either the trigger is the lever that releases the
hammer and discharges a bullet, or it is not. J.A. 71. Such a
concession shows that Plaintiffs’ definition is unworkable,
internally inconsistent, and counterintuitive.

By contrast, the Bump Stock Rule’s definition would
encompass this mechanical hand device. In response to
comments about different trigger activation methods, the
Bureau added the phrase “and analogous motions” to the final
rule, thereby including devices that function via “a push or
other method of initiating the firing cycle.” 83 Fed. Reg. at
66,534–35. In this scenario, pushing the button neatly qualifies
as an “analogous motion.”
 23
Even assuming, moreover, that it were appropriate to
reconceive of the trigger on the firearm with the mechanical
hand device to be the button that activates the mechanical
hand’s trigger finger, imagine another type of firearm that
contains no such button but only a standard trigger, and that
operates such that the shooter’s pull of the trigger causes an
internal motor to initiate a repeated movement of the trigger
back and forth—with a release of the hammer each time—
producing a continuous, automatic series of shots. 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
machine gun 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. The weapon is similar to the Akins
Accelerator, see 83 Fed. Reg. at 66,517, except that the
hypothetical weapon involves an internal motor that causes the
trigger to automatically move back and forth after the initial
pull, as opposed to an internal spring that causes the barrel to
automatically move back and forth into a stationary trigger
finger after the initial pull: in either case, the trigger continues
to move, and shots continue to fire, without any additional
input from the shooter.

Plaintiffs believe that the Akins Accelerator was
mistakenly dubbed a machine gun because it, like a bump stock
 24
device, fires only one round with each mechanical movement
of the trigger. See Appellants’ Opening Br. 8 n.2. The same is
true of the hypothetical weapon described here. And insofar as
Plaintiffs might nonetheless attempt to draw a distinction
between the two, it is hard to see how one would involve a
“single function of the trigger” and the other would not: with
both, the shooter’s initial pull of the trigger initiates an
automatic sequence (caused by an internal motor, on one hand,
and an internal spring, on the other) whereby the weapon’s
trigger then continuously moves back and forth, causing
additional shots to fire, without any further input by the
shooter. And with both, that automatic sequence continues
until ammunition is exhausted; the weapon malfunctions; or the
shooter takes a new action to stop that sequence. In sum,
Plaintiffs’ proffered interpretation of “single function of the
trigger” is unsound.

Plaintiffs’ interpretation of “automatically” is no less
problematic. They interpret “automatically” as “self-acting” or
requiring only “the expressly specified initiating action” before
operating on its own. Appellants’ Opening Br. 27–28. In their
view, bump stocks do not operate automatically because the
shooter must maintain constant forward pressure on the bump
stock with his non-trigger hand to continue firing. This
definition would remove what Plaintiffs would describe as a
prototypical machine gun from the realm of “automatic,” as the
shooter must both pull the trigger and keep his finger depressed
on the trigger to continue firing. Once the force is removed
from the trigger, firing ceases. Per Plaintiffs’ definition, only
a gun that required no human input to fire more than a single
shot would qualify as a machine gun. By this logic, we would
no longer characterize even the prototypical machine gun as a
“machine gun,” given the extent of rearward pressure on the
trigger required to operate it. That cannot be right.
 25
Plaintiffs also point to Congress’s decision to remove “or
semiautomatically” from the definition of machine gun in the
1968 Gun Control Act as evidence that “automatically” must
be interpreted narrowly in their favor. Appellants’ Opening Br.
30–32. According to Plaintiffs, the significance of this erasure
is linked to the Treasury Department’s 1955 ruling that crank-
operated Gatling guns were not machine guns. See Revenue
Ruling 55-528, 1955 WL 9410, at *1 (Jan. 1, 1955). Taken
together, Plaintiffs argue that Congress indicated its approval
of this ruling by removing “or semiautomatically” from the
statute, thus advancing a narrow interpretation of the statute.
Yet, Plaintiffs have not offered any evidence of the link
between the 1955 ruling and Congress’s 1968 definition
amendment. Moreover, the exclusion of semiautomatic
weapons from the Gun Control Act is not implicated here; we
are concerned only with the conversion of semiautomatic
weapons to fully automatic firearms.

Finally, Plaintiffs’ fear that all semiautomatic weapons
will be subject to regulation because they can be modified with
everyday items, like belt loops, to fire automatically is
unfounded. Unlike a bump stock, a rubber band or belt loop is
not automatic because it is not self-regulating. Rather than
harnessing the firearm’s recoil energy from a rubber band or
belt loop in a linear path to engage in a continuous firing
sequence, the shooter must harness and direct the recoil energy
himself. Bump Stock Rule, 83 Fed. Reg. at 66,533. As the
Bureau explained, “the belt loop or similar manual method
requires the shooter to control the distance that the firearm
recoils and the movement along the plane on which the firearm
recoils.” Id. Harnessing the recoil energy without an automatic
device requires a great deal of skill and renders it exponentially
more difficult to bump fire. These everyday devices are
“objectively different” from bump stocks and do not qualify as
machine guns under the Bureau’s interpretation. Id.
 26

IV.

Plaintiffs also urge us to apply the rule of lenity. The rule
of lenity instructs courts to resolve ambiguity in favor of a
criminal defendant, but it “only applies if, after considering
text, structure, history, and purpose, there remains a grievous
ambiguity or uncertainty in the statute that the Court must
simply guess at what Congress intended.” Maracich v. Spears,
570 U.S. 48, 76 (2013). See also Staples, 511 U.S. at 619 n.17
(applying rule of lenity was unnecessary where meaning could
be derived through interpretive tools).

It is only where the Court has exhausted “everything from
which aid can be derived” that lenity plays a role. Muscarello
v. United States, 524 U.S. 125, 138 (1998) (internal quotation
marks and citations omitted). For example, in United States v.
Bass, the Court applied the rule of lenity where it could not
decisively interpret the prosecution’s evidentiary burden from
Title VII of the Omnibus Crime Control and Safe Streets Act
of 1968. 404 U.S. 336, 337–38, 347. Given the lack of clear
statutory language, legislative history, and a clear statement of
congressional purpose, the Court resorted to lenity to approve
a narrower construction in this instance. Id. at 347–50. See
also United States v. Universal C.I.T. Credit Corp., 344 U.S.
218, 221 (1952) (turning to lenity in Fair Labor Standards Act
case where “literal reading” of text did not illuminate statutory
construction). Fortunately, we are not left to “guess at” the
meaning of the text at issue here, see Maracich, 570 U.S. at 76,
given the array of tools at our disposal, including the statute’s
plain language, prior case law, contemporaneous
understandings, and congressional purpose. As a result, we are
not left with the type of “grievous ambiguity,” see id., that
would require the rule of lenity’s application here.
 27
To be sure, the Bureau’s interpretation is not the only
possible interpretation of the statute. But most importantly, the
task before us is to find the best interpretation of the statute,
which does not mean that it is the only “permissible” or
reasonable interpretation. See Edelman, 535 U.S. at 114 & n.8
(internal quotation marks omitted). Further, the predominant
concern among those skeptical of upholding the Bureau’s
interpretation is their view that it is inappropriate to use the
Chevron framework to uphold the regulation, which is not at
issue here. See Guedes v. ATF, 140 S. Ct. 789, 789–91 (2020)
(Mem.) (Gorsuch, J., concurring in denial of certiorari)
(questioning application of Chevron deference to the rule
before us); Gun Owners of America, Inc. v. Garland, 19 F. 4th
890, 925 (6th Cir. 2021) (Murphy, J., dissenting) (critiquing
circuit courts for failing to interpret statute before turning to
Chevron); Aposhian v. Wilkinson, 989 F.3d 890, 894–96 (2021)
(Mem.) (Tymkovich, J., dissenting) (same). And it is worth
noting that every circuit to have considered this question has so
far upheld the Bump Stock Rule. See Cargill v. Garland, 20
F.4th 1004 (5th Cir. 2021), vacated and en banc granted, --
F.4th -- (2022); Gun Owners v. Garland, 19 F.4th 890 (6th Cir.
2021) (en banc); Aposhian v. Barr, 958 F.3d 969 (10th Cir.
2020), en banc granted but previous order reinstated, 989 F.3d
890 (Mem.).

The manufacturer of one of the bump stock devices owned
by Plaintiffs once promoted that its product enabled “Spraying
900 rounds in 60 seconds.” What is Bump Fire, BUMP FIRE
SYS., https://bit.ly/3PdRTNH. We join those circuits in
concluding that these devices, which enable such prodigious
rapid-fire capability upon a pull of the trigger, fall within the
definition of “machine gun” in the National Firearms Act and
Gun Control Act. For the foregoing reasons, the District
Court’s judgment is affirmed.
28
So ordered.
 29
APPENDIX

Figure 1: The shooter pushes the firing unit so that it slides
forward inside the bump stock and he pulls the trigger.

Figure 2: After the first shot, the shooter’s finger rests against
the extension ledge of the bump stock, which “constrains” the
recoil and the opposing forward force so that the firing unit
slides in a linear direction, propelling the firing unit against the
stationary finger, causing the firing cycle to repeat.