(Slip Opinion)              OCTOBER TERM, 2023                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 

.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

 GARLAND, ATTORNEY GENERAL, ET AL. v. CARGILL

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
                  THE FIFTH CIRCUIT

    No. 22–976.      Argued February 28, 2024—Decided June 14, 2024
The National Firearms Act of 1934 defines a “machinegun” as “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.” 

(b). With a ma-
  chinegun, a shooter can fire multiple times, or even continuously, by
  engaging the trigger only once. This capability distinguishes a ma-
  chinegun from a semiautomatic firearm. With a semiautomatic fire-
  arm, the shooter can fire only one time by engaging the trigger. Using
  a technique called bump firing, shooters can fire semiautomatic fire-
  arms at rates approaching those of some machineguns. A shooter who
  bump fires a rifle uses the firearm’s recoil to help rapidly manipulate
  the trigger. Although bump firing does not require any additional
  equipment, a “bump stock” is an accessory designed to make the tech-
  nique easier. A bump stock does not alter the basic mechanics of bump
  firing, and the trigger still must be released and reengaged to fire each
  additional shot.
     For many years, the Bureau of Alcohol, Tobacco, Firearms and Ex-
  plosives (ATF) consistently took the position that semiautomatic rifles
  equipped with bump stocks were not machineguns under §5845(b).
  ATF abruptly changed course when a gunman using semiautomatic
  rifles equipped with bump stocks fired hundreds of rounds into a crowd
  in Las Vegas, Nevada, killing 58 people and wounding over 500 more.
  ATF subsequently proposed a rule that would repudiate its previous
  guidance and amend its regulations to “clarify” that bump stocks are
  machineguns. 

. ATF’s Rule ordered owners of
  bump stocks either to destroy or surrender them to ATF to avoid crim-
  inal prosecution.
     Michael Cargill surrendered two bump stocks to ATF under protest,
2                          GARLAND v. CARGILL

                                   Syllabus

    then filed suit to challenge the Rule under the Administrative Proce-
    dure Act. As relevant, Cargill alleged that ATF lacked statutory au-
    thority to promulgate the Rule because bump stocks are not “ma-
    chinegun[s]” as defined in §5845(b). After a bench trial, the District
    Court entered judgment for ATF. The Fifth Circuit initially affirmed,
    but reversed after rehearing en banc. A majority agreed that §5845(b)
    is ambiguous as to whether a semiautomatic rifle equipped with a
    bump stock fits the statutory definition of a machinegun and resolved
    that ambiguity in Cargill’s favor.
    Held: ATF exceeded its statutory authority by issuing a Rule that clas-
    sifies a bump stock as a “machinegun” under §5845(b). Pp. 6–19.
       (a) A semiautomatic rifle equipped with a bump stock is not a “ma-
    chinegun” as defined by §5845(b) because: (1) it cannot fire more than
    one shot “by a single function of the trigger” and (2) even if it could, it
    would not do so “automatically.” ATF therefore exceeded its statutory
    authority by issuing a Rule that classifies bump stocks as ma-
    chineguns. P. 6.
       (b) A semiautomatic rifle equipped with a bump stock does not fire
    more than one shot “by a single function of the trigger.” The phrase
    “function of the trigger” refers to the mode of action by which the trig-
    ger activates the firing mechanism. No one disputes that a semiauto-
    matic rifle without a bump stock is not a machinegun because a
    shooter must release and reset the trigger between every shot. And,
    any subsequent shot fired after the trigger has been released and reset
    is the result of a separate and distinct “function of the trigger.” Noth-
    ing changes when a semiautomatic rifle is equipped with a bump stock.
    Between every shot, the shooter must release pressure from the trigger
    and allow it to reset before reengaging the trigger for another shot. A
    bump stock merely reduces the amount of time that elapses between
    separate “functions” of the trigger.
       ATF argues that a shooter using a bump stock must pull the trigger
    only one time to initiate a bump-firing sequence of multiple shots. This
    initial trigger pull sets off a sequence—fire, recoil, bump, fire—that
    allows the weapon to continue firing without additional physical ma-
    nipulation of the trigger by the shooter. This argument rests on the
    mistaken premise that there is a difference between the shooter flexing
    his finger to pull the trigger and pushing the firearm forward to bump
    the trigger against his stationary trigger. Moreover, ATF’s position is
    logically inconsistent because its reasoning would also mean that a
    semiautomatic rifle without a bump stock is capable of firing more
    than one shot by a “single function of the trigger.” Yet, ATF agrees
    that is not the case. ATF’s argument is thus at odds with itself. Pp.
    7–14.
       (c) Even if a semiautomatic rifle with a bump stock could fire more
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                              Syllabus

than one shot “by a single function of the trigger,” it would not do so
“automatically.” Section 5845(b) specifies the precise action that must
“automatically” cause a weapon to fire “more than one shot”—a “single
function of the trigger.” If something more than a “single function of
the trigger” is required to fire multiple shots, the weapon does not sat-
isfy the statutory definition. Firing multiple shots using a semiauto-
matic rifle with a bump stock requires more than a single function of
the trigger. A shooter must maintain forward pressure on the rifle’s
front grip with his nontrigger hand. Without this ongoing manual in-
put, a semiautomatic rifle with a bump stock will not fire multiple
shots.
   ATF counters that machineguns also require continuous manual in-
put from a shooter: The shooter must both engage the trigger and keep
it pressed down to continue shooting. ATF argues there is no mean-
ingful difference between holding down the trigger of a traditional ma-
chinegun and maintaining forward pressure on the front grip of a sem-
iautomatic rifle with a bump stock. This argument ignores that
Congress defined a machinegun by what happens “automatically” “by
a single function of the trigger.” Simply pressing and holding the trig-
ger down on a fully automatic rifle is not manual input in addition to
a trigger’s function. By contrast, pushing forward on the front grip of
a semiautomatic rifle equipped with a bump stock is not part of func-
tioning the trigger.
   Moreover, a semiautomatic rifle with a bump stock is indistinguish-
able from the Ithaca Model 37 shotgun, a weapon the ATF concedes
cannot fire multiple shots “automatically.” ATF responds that a
shooter is less physically involved with operating a bump-stock
equipped rifle than operating the Model 37. It explains that once a
shooter pulls the rifle’s trigger a single time, the bump stock harnesses
the firearm’s recoil energy in a continuous back-and-forth cycle that
allows the shooter to attain continuous firing. But, even if one aspect
of a weapon’s operation could be seen as “automatic,” that would not
mean the weapon “shoots . . . automatically more than one shot . . . by
a single function of the trigger.” §5845(b) (emphasis added). Pp. 14–
17.
   (d) Abandoning the text, ATF attempts to shore up its position by
relying on the presumption against ineffectiveness. That presumption
weighs against interpretations of a statute that would “rende[r] the
law in a great measure nugatory, and enable offenders to elude its pro-
visions in the most easy manner.” The Emily, 

. In
ATF’s view, Congress “restricted machineguns because they eliminate
the manual movements that a shooter would otherwise need to make
in order to fire continuously” at a high rate of fire, as bump stocks do.
Brief for Petitioners 40. So, ATF reasons, concluding that bump stocks
4                          GARLAND v. CARGILL

                                  Syllabus

    are lawful “simply because the [trigger] moves back and forth . . . would
    exalt artifice above reality and enable evasion of the federal ma-
    chinegun ban.” 

 at 41–42. The presumption against ineffectiveness
    cannot do the work that ATF asks of it. Interpreting §5845(b) to ex-
    clude semiautomatic rifles equipped with bump stocks comes nowhere
    close to making the statute useless. Pp. 17–19.

, affirmed.

   THOMAS, J. delivered the opinion of the Court, in which ROBERTS, C. J.,
and ALITO, GORSUCH, KAVANAUGH, and BARRETT, JJ., joined. ALITO, J.,
filed a concurring opinion. SOTOMAYOR, J., filed a dissenting opinion, in
which KAGAN and JACKSON, JJ., joined.
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                             Opinion of the Court

     NOTICE: This opinion is subject to formal revision before publication in the
     United States Reports. Readers are requested to notify the Reporter of
     Decisions, Supreme Court of the United States, Washington, D. C. 20543,
     pio@supremecourt gov, of any typographical or other formal errors.


SUPREME COURT OF THE UNITED STATES
                                   _________________

                                   No. 22–976
                                   _________________


MERRICK B. GARLAND, ATTORNEY GENERAL, ET AL.,
      PETITIONERS v. MICHAEL CARGILL
 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
            APPEALS FOR THE FIFTH CIRCUIT
                                 [June 14, 2024]

   JUSTICE THOMAS delivered the opinion of the Court.
   Congress has long restricted access to “ ‘machinegun[s],’ ”
a category of firearms defined by the ability to “shoot, auto-
matically more than one shot . . . by a single function of the
trigger.” 

(b); see also 

(o).
Semiautomatic firearms, which require shooters to reen-
gage the trigger for every shot, are not machineguns. This
case asks whether a bump stock—an accessory for a semi-
automatic rifle that allows the shooter to rapidly reengage
the trigger (and therefore achieve a high rate of fire)—con-
verts the rifle into a “machinegun.” We hold that it does not
and therefore affirm.
                              I
                             A
  Under the National Firearms Act of 1934, a “ma-
chinegun” is “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.” §5845(b). The statutory definition
also includes “any part designed and intended . . . for use in
2                   GARLAND v. CARGILL

                      Opinion of the Court

converting a weapon into a machinegun.” Ibid. With a ma-
chinegun, a shooter can fire multiple times, or even contin-
uously, by engaging the trigger only once. This capability
distinguishes a machinegun from a semiautomatic firearm.
With a semiautomatic firearm, the shooter can fire only one
time by engaging the trigger. The shooter must release and
reengage the trigger to fire another shot. Machineguns can
ordinarily achieve higher rates of fire than semiautomatic
firearms because the shooter does not need to release and
reengage the trigger between shots.
   Shooters have devised techniques for firing semiauto-
matic firearms at rates approaching those of some ma-
chineguns. One technique is called bump firing. A shooter
who bump fires a rifle uses the firearm’s recoil to help rap-
idly manipulate the trigger. The shooter allows the recoil
from one shot to push the whole firearm backward. As the
rifle slides back and away from the shooter’s stationary
trigger finger, the trigger is released and reset for the next
shot. Simultaneously, the shooter uses his nontrigger hand
to maintain forward pressure on the rifle’s front grip. The
forward pressure counteracts the recoil and causes the fire-
arm (and thus the trigger) to move forward and “bump” into
the shooter’s trigger finger. This bump reengages the trig-
ger and causes another shot to fire, and so on.
   Bump firing is a balancing act. The shooter must main-
tain enough forward pressure to ensure that he will bump
the trigger with sufficient force to engage it. But, if the
shooter applies too much forward pressure, the rifle will not
slide back far enough to allow the trigger to reset. The right
balance produces a reciprocating motion that permits the
shooter to repeatedly engage and release the trigger in
rapid succession.
   Although bump firing does not require any additional
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                           Opinion of the Court

equipment, there are accessories designed to make the tech-
nique easier. A “bump stock” is one such accessory.1 It re-
places a semiautomatic rifle’s stock (the back part of the ri-
fle that rests against the shooter’s shoulder) with a plastic
casing that allows every other part of the rifle to slide back
and forth. This casing helps manage the back-and-forth
motion required for bump firing. A bump stock also has a
ledge to keep the shooter’s trigger finger stationary. A
bump stock does not alter the basic mechanics of bump fir-
ing. As with any semiautomatic firearm, the trigger still
must be released and reengaged to fire each additional shot.
                              B
   The question in this case is whether a bump stock trans-
forms a semiautomatic rifle into a “machinegun,” as defined
by §5845(b). For many years, the Bureau of Alcohol, To-
bacco, Firearms and Explosives (ATF) took the position that
semiautomatic rifles equipped with bump stocks were not
machineguns under the statute. On more than 10 separate
occasions over several administrations, ATF consistently
concluded that rifles equipped with bump stocks cannot
“automatically” fire more than one shot “by a single func-
tion of the trigger.” See App. 16–68. In April 2017, for ex-
ample, ATF explained that a rifle equipped with a bump
stock does not “operat[e] automatically” because “forward
pressure must be applied with the support hand to the for-
ward handguard.” Id., at 66. And, because the shooter
slides the rifle forward in the stock “to fire each shot, each
succeeding shot fir[es] with a single trigger function.” Id.,
at 67.
   ATF abruptly reversed course in response to a mass
shooting in Las Vegas, Nevada. In October 2017, a gunman
——————
  1 Some bump stocks (called mechanical bump stocks) rely on an inter-

nal spring, rather than forward pressure from the shooter’s nontrigger
hand, to force the rifle and trigger forward after recoil. These devices are
not at issue in this case.
4                    GARLAND v. CARGILL

                       Opinion of the Court

fired on a crowd attending an outdoor music festival in Las
Vegas, killing 58 people and wounding over 500 more. The
gunman equipped his weapons with bump stocks, which al-
lowed him to fire hundreds of rounds in a matter of minutes.
   This tragedy created tremendous political pressure to
outlaw bump stocks nationwide. Within days, Members of
Congress proposed bills to ban bump stocks and other de-
vices “designed . . . to accelerate the rate of fire of a semiau-
tomatic rifle.” S. 1916, 115th Cong., 1st Sess., §2 (2017); see
also H. R. 3947, 115th Cong., 1st Sess. (2017); H. R. 3999,
115th Cong., 1st Sess. (2017). None of these bills became
law. Similar proposals in the intervening years have also
stalled. See, e.g., H. R. 396, 118th Cong., 1st Sess. (2023);
S. 1909, 118th Cong., 1st Sess. (2023); H. R. 5427, 117th
Cong., 1st Sess. (2021).
   While the first wave of bills was pending, ATF began con-
sidering whether to reinterpret §5845(b)’s definition of “ma-
chinegun” to include bump stocks. It proposed a rule that
would amend its regulations to “clarify” that bump stocks
are machineguns. 

 (2018). ATF’s about-
face drew criticism from some observers, including those
who agreed that bump stocks should be banned. Senator
Dianne Feinstein, for example, warned that ATF lacked
statutory authority to prohibit bump stocks, explaining
that the proposed regulation “ ‘hinge[d] on a dubious analy-
sis’ ” and that the “ ‘gun lobby and manufacturers [would]
have a field day with [ATF’s] reasoning’ ” in court. State-
ment on Regulation To Ban Bump Stocks (Mar. 23, 2018).
She asserted that “ ‘legislation is the only way to ban bump
stocks.’ ” 

   ATF issued its final Rule in 2018. 

.
The agency’s earlier regulations simply restated §5845(b)’s
statutory definition. Ibid. The final Rule amended those
regulations by adding the following language:
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                      Opinion of the Court

    “[T]he term ‘automatically’ as it modifies ‘shoots, is de-
    signed to shoot, or can be readily restored to shoot,’
    means functioning as the result of a self-acting or self-
    regulating mechanism that allows the firing of multiple
    rounds through a single function of the trigger; and
    ‘single function of the trigger’ means a single pull of the
    trigger and analogous motions. The term ‘machinegun’
    includes a bump-stock-type device, i.e., a device that al-
    lows a semi-automatic firearm to shoot more than one
    shot with a single pull of the trigger by harnessing the
    recoil energy of the semi-automatic firearm to which it
    is affixed so that the trigger resets and continues firing
    without additional physical manipulation of the trigger
    by the shooter.” 

 at 66553–66554.
The final Rule also repudiated ATF’s previous guidance
that bump stocks did not qualify as “machineguns” under
§5845(b). Id., at 66530–66531. And, it ordered owners of
bump stocks to destroy them or surrender them to ATF
within 90 days. Id., at 66530. Bump-stock owners who
failed to comply would be subject to criminal prosecution.
Id., at 66525; see also 

(o)(1).
                             C
  Michael Cargill surrendered two bump stocks to ATF un-
der protest. He then filed suit to challenge the final Rule,
asserting a claim under the Administrative Procedure Act.
As relevant, Cargill alleged that ATF lacked statutory au-
thority to promulgate the final Rule because bump stocks
are not “machinegun[s]” as defined in §5845(b). After a
bench trial, the District Court entered judgment for ATF.
The court concluded that “a bump stock fits the statutory
definition of a ‘machinegun.’ ”      Cargill v. Barr, 

, 1194 (WD Tex. 2020).
  The Court of Appeals initially affirmed, 

(CA5 2021), but later reversed after rehearing en banc, 

 (CA5 2023). A majority agreed, at a minimum,
6                      GARLAND v. CARGILL

                         Opinion of the Court

that §5845(b) is ambiguous as to whether a semiautomatic
rifle equipped with a bump stock fits the statutory defini-
tion of a machinegun. And, the majority concluded that the
rule of lenity required resolving that ambiguity in Cargill’s
favor. Id., at 469; see also id., at 450, n. An eight-judge
plurality determined that the statutory definition of “ma-
chinegun” unambiguously excludes such weapons. A semi-
automatic rifle equipped with a bump stock, the plurality
reasoned, fires only one shot “each time the trigger ‘acts,’ ”
id., at 459, and so does not fire “more than one shot . . . by
a single function of the trigger,” §5845(b). The plurality
also concluded that a bump stock does not enable a semiau-
tomatic rifle to fire more than one shot “automatically” be-
cause the shooter must “maintain manual, forward pres-
sure on the barrel.” Id., at 463.
   We granted certiorari, 

 (2023), to address a
split among the Courts of Appeals regarding whether bump
stocks meet §5845(b)’s definition of “machinegun.”2 We now
affirm.
                               II
  Section 5845(b) defines a “machinegun” as any weapon
capable of firing “automatically more than one shot . . . by
a single function of the trigger.” We hold that a semiauto-
matic rifle equipped with a bump stock is not a “ma-
chinegun” because it cannot fire more than one shot “by a
single function of the trigger.” And, even if it could, it would
not do so “automatically.” ATF therefore exceeded its stat-
utory authority by issuing a Rule that classifies bump
stocks as machineguns.


——————
  2 See, e.g., Hardin v. Bureau of Alcohol, Tobacco, Firearms and Explo-

sives, 

 (CA6 2023); Guedes v. Bureau of Alcohol, Tobacco,
Firearms and Explosives, 

 (CADC 2022); Aposhian v. Barr,

 (CA10 2020).
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                      Opinion of the Court

                               A
   A semiautomatic rifle equipped with a bump stock does
not fire more than one shot “by a single function of the trig-
ger.” With or without a bump stock, a shooter must release
and reset the trigger between every shot. And, any subse-
quent shot fired after the trigger has been released and re-
set is the result of a separate and distinct “function of the
trigger.” All that a bump stock does is accelerate the rate
of fire by causing these distinct “function[s]” of the trigger
to occur in rapid succession.
   As always, we start with the statutory text, which refers
to “a single function of the trigger.” The “function” of an
object is “the mode of action by which it fulfils its purpose.”
4 Oxford English Dictionary 602 (1933); see also American
Heritage Dictionary 533 (1969) (“The natural or proper ac-
tion for which a . . . mechanism . . . is fitted or employed”).
And, a “trigger” is an apparatus, such as a “movable catch
or lever,” that “sets some force or mechanism in action.” 11
Oxford English Dictionary, at 357; see also American Her-
itage Dictionary, at 1371 (“The lever pressed by the finger
to discharge a firearm” or “[a]ny similar device used to re-
lease or activate a mechanism”); Webster’s New Interna-
tional Dictionary 2711 (2d ed. 1934) (“A piece, as a lever,
connected with a catch or detent as a means of releasing it;
specif., Firearms, the part of a lock moved by the finger to
release the cock in firing”). The phrase “function of the trig-
ger” thus refers to the mode of action by which the trigger
activates the firing mechanism. For most firearms, includ-
ing the ones at issue here, the trigger is a curved metal
lever. On weapons with these standard trigger mecha-
nisms, the phrase “function of the trigger” means the phys-
ical trigger movement required to shoot the firearm.
   No one disputes that a semiautomatic rifle without a
bump stock is not a machinegun because it fires only one
shot per “function of the trigger.” That is, engaging the trig-
8                      GARLAND v. CARGILL

                         Opinion of the Court

ger a single time will cause the firing mechanism to dis-
charge only one shot. To understand why, it is helpful to
consider the mechanics of the firing cycle for a semiauto-
matic rifle. Because the statutory definition is keyed to a
“function of the trigger,” only the trigger assembly is rele-
vant for our purposes. Although trigger assemblies for sem-
iautomatic rifles vary, the basic mechanics are generally
the same. The following series of illustrations depicts how
the trigger assembly on an AR–15 style semiautomatic rifle
works.3 In each illustration, the front of the rifle (i.e., the
barrel) would be pointing to the left.
  We begin with an overview of the relevant components:




                               Figure 1.

The trigger is a simple lever that moves backward and for-
ward. P. Sweeney, Gunsmithing the AR–15, p. 131 (2016).
The square point at the top left edge of the trigger locks into
a notch at the bottom of the hammer. P. Sweeney, Gun-
smithing: Rifles 269 (1999). The hammer is a spring-loaded
part that swings forward toward the barrel and strikes the
firing pin, causing a shot to fire. 

 The disconnector is
the component responsible for resetting the hammer to its
——————
  3 These illustrations are found in the Brief for FPC Action Foundation

as Amicus Curiae 14–15.
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                      Opinion of the Court

original position after a shot is fired. 

  We turn next to how these components operate:




                            Figure 2.

When the shooter engages the trigger by moving it back-
ward (as indicated by the arrow), the square point of the
trigger pivots downward and out of the notch securing the
hammer. 

 This movement releases the spring-loaded
hammer, allowing it to swing forward. 

                            Figure 3.

At the top of the hammer’s rotation, it strikes the firing pin,
causing the weapon to fire a single shot. See 

10                 GARLAND v. CARGILL

                     Opinion of the Court




                          Figure 4.

The firearm then ejects the spent cartridge from the cham-
ber and loads a new one in its place. D. Long, The Complete
AR–15/M16 Sourcebook 206 (2001). The mechanism that
performs this task swings the hammer backward at the
same time. 

                          Figure 5.

As the hammer swings backward, it latches onto the discon-
nector. Sweeney, Gunsmithing: Rifles, at 269. This latch-
ing (circled above) prevents the hammer from swinging for-
ward again after a new cartridge is loaded into the
chamber. 

 The disconnector will hold the hammer in
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                          Opinion of the Court

that position for as long as the shooter holds the trigger
back, thus preventing the firearm from firing another shot.4

                               Figure 6.

Finally, when the shooter takes pressure off the trigger and
allows it to move forward (as indicated by the arrow), the
hammer slips off the disconnector just as the square point
of the trigger rises into the notch on the hammer (circled
above). 

 The trigger mechanism is thereby reset to the
original position shown in Figure 1. A semiautomatic rifle
must complete this cycle for each shot fired.5
   ATF does not dispute that this complete process is what
constitutes a “single function of the trigger.” A shooter may
fire the weapon again after the trigger has reset, but only
——————
   4 Machinegun variants of the AR–15 style rifle include an additional

component known as an auto sear. The auto sear catches the hammer
as it swings backwards, but will release it again once a new cartridge is
loaded if the trigger is being held back. P. Sweeney, 1 The Gun Digest
Book of the AR–15, p. 38 (2005). An auto sear thus permits a shooter to
fire multiple shots while engaging the trigger only once. ATF has accord-
ingly recognized that modifying a semiautomatic rifle or handgun with
an auto sear converts it into a machinegun. See ATF Ruling 81–4.
   5 An animated graphic that displays the relevant movements is avail-

able at https://www.supremecourt.gov/media/images/AR-15.gif .
12                   GARLAND v. CARGILL

                      Opinion of the Court

by engaging the trigger a second time and thereby initiating
a new firing cycle. For each shot, the shooter must engage
the trigger and then release the trigger to allow it to reset.
Any additional shot fired after one cycle is the result of a
separate and distinct “function of the trigger.”
   Nothing changes when a semiautomatic rifle is equipped
with a bump stock. The firing cycle remains the same. Be-
tween every shot, the shooter must release pressure from
the trigger and allow it to reset before reengaging the trig-
ger for another shot. A bump stock merely reduces the
amount of time that elapses between separate “functions”
of the trigger. The bump stock makes it easier for the
shooter to move the firearm back toward his shoulder and
thereby release pressure from the trigger and reset it. And,
it helps the shooter press the trigger against his finger very
quickly thereafter. A bump stock does not convert a semi-
automatic rifle into a machinegun any more than a shooter
with a lightning-fast trigger finger does. Even with a bump
stock, a semiautomatic rifle will fire only one shot for every
“function of the trigger.” So, a bump stock cannot qualify
as a machinegun under §5845(b)’s definition.
   Although ATF agrees on a semiautomatic rifle’s mechan-
ics, it nevertheless insists that a bump stock allows a sem-
iautomatic rifle to fire multiple shots “by a single function
of the trigger.” ATF starts by interpreting the phrase “sin-
gle function of the trigger” to mean “a single pull of the trig-
ger and analogous motions.” 

. A shooter
using a bump stock, it asserts, must pull the trigger only
one time to initiate a bump-firing sequence of multiple
shots. 

. This initial trigger pull sets off a se-
quence—fire, recoil, bump, fire—that allows the weapon to
continue firing “without additional physical manipulation
of the trigger by the shooter.” 

 According to ATF, all
the shooter must do is keep his trigger finger stationary on
the bump stock’s ledge and maintain constant forward pres-
sure on the front grip to continue firing. The dissent offers
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                          Opinion of the Court

similar reasoning.        See post, at 7–9 (opinion of
SOTOMAYOR, J.).
   This argument rests on the mistaken premise that there
is a difference between a shooter flexing his finger to pull
the trigger and a shooter pushing the firearm forward to
bump the trigger against his stationary finger. ATF and
the dissent seek to call the shooter’s initial trigger pull a
“function of the trigger” while ignoring the subsequent
“bumps” of the shooter’s finger against the trigger before
every additional shot. But, §5845(b) does not define a ma-
chinegun based on what type of human input engages the
trigger—whether it be a pull, bump, or something else. Nor
does it define a machinegun based on whether the shooter
has assistance engaging the trigger. The statutory defini-
tion instead hinges on how many shots discharge when the
shooter engages the trigger. And, as we have explained, a
semiautomatic rifle will fire only one shot each time the
shooter engages the trigger—with or without a bump
stock.6 Supra, at 7–12.
   In any event, ATF’s argument cannot succeed on its own
terms. The final Rule defines “function of the trigger” to
include not only “a single pull of the trigger” but also any
“analogous motions.” 

. ATF concedes
that one such analogous motion that qualifies as a single
function of the trigger is “sliding the rifle forward” to bump
the trigger. Brief for Petitioners 22. But, if that is true,
then every bump is a separate “function of the trigger,” and
semiautomatic rifles equipped with bump stocks are there-
fore not machineguns. ATF resists the natural implication
——————
   6 The dissent says that we “resis[t]” the “ordinary understanding of the

term ‘function of the trigger’ with two technical arguments.” Post, at 10.
But, the arguments it refers to explain why, even assuming a semiauto-
matic rifle equipped with a bump stock could fire more than one shot by
a single function of the trigger, it could not do so “automatically.” See
infra, at 14–17. Those arguments have nothing to do with our explana-
tion of what a “single function of the trigger” means. 

14                  GARLAND v. CARGILL

                      Opinion of the Court

of its reasoning, insisting that the bumping motion is a
“function of the trigger” only when it initiates, but not when
it continues, a firing sequence. But, Congress did not write
a statutory definition of “machinegun” keyed to when a fir-
ing sequence begins and ends. Section 5845(b) asks only
whether a weapon fires more than one shot “by a single
function of the trigger.”
   Finally, the position that ATF and the dissent endorse is
logically inconsistent. They reason that a semiautomatic
rifle equipped with a bump stock fires more than one shot
by a single function of the trigger because a shooter “need
only pull the trigger and maintain forward pressure” to “ac-
tivate continuous fire.” Post, at 10; see also Brief for Peti-
tioners 23. If that is correct, however, then the same should
be true for a semiautomatic rifle without a bump stock. Af-
ter all, as the dissent and ATF themselves acknowledge, a
shooter manually bump firing a semiautomatic rifle can
achieve continuous fire by holding his trigger finger station-
ary and maintaining forward pressure with his nontrigger
hand. See post, at 5; 

. Yet, they agree
that a semiautomatic rifle without a bump stock “fires only
one shot each time the shooter pulls the trigger.” Post, at
4; see also 

. Their argument is thus at
odds with itself.
   We conclude that semiautomatic rifle equipped with a
bump stock is not a “machinegun” because it does not fire
more than one shot “by a single function of the trigger.”
                              B
  A bump stock is not a “machinegun” for another reason:
Even if a semiautomatic rifle with a bump stock could fire
more than one shot “by a single function of the trigger,” it
would not do so “automatically.” Section 5845(b) asks
whether a weapon “shoots . . . automatically more than one
shot . . . by a single function of the trigger.” The statute
thus specifies the precise action that must “automatically”
                      Cite as: 

 (2024)                       15

                           Opinion of the Court

cause a weapon to fire “more than one shot”—a “single func-
tion of the trigger.” If something more than a “single func-
tion of the trigger” is required to fire multiple shots, the
weapon does not satisfy the statutory definition. As Judge
Henderson put it, the “statutory definition of ‘machinegun’
does not include a firearm that shoots more than one round
‘automatically’ by a single pull of the trigger AND THEN
SOME.” Guedes v. Bureau of Alcohol, Tobacco, Firearms
and Explosives, 

 (CADC 2019) (opinion con-
curring in part and dissenting in part).
   Firing multiple shots using a semiautomatic rifle with a
bump stock requires more than a single function of the trig-
ger. A shooter must also actively maintain just the right
amount of forward pressure on the rifle’s front grip with his
nontrigger hand. See supra, at 2–3. Too much forward
pressure and the rifle will not slide back far enough to re-
lease and reset the trigger, preventing the rifle from firing
another shot. Too little pressure and the trigger will not
bump the shooter’s trigger finger with sufficient force to fire
another shot. Without this ongoing manual input, a semi-
automatic rifle with a bump stock will not fire multiple
shots. Thus, firing multiple shots requires engaging the
trigger one time—and then some.7
   ATF and the dissent counter that machineguns also re-
quire continuous manual input from a shooter: He must
——————
   7 The dissent seemingly concedes this point, repeatedly recognizing

that the shooter must both pull the trigger and maintain forward pres-
sure on the front grip. See, e.g., post, at 6 (“[A] single pull of the trigger
provides continuous fire as long as the shooter maintains forward pres-
sure on the gun”); ibid. (“A bump-stock-equipped semiautomatic rifle is
a machinegun because . . . a shooter can . . . fire continuous shots without
any human input beyond maintaining forward pressure”); post, at 10
(“[A] shooter of a bump-stock-equipped AR–15 need only pull the trigger
and maintain forward pressure”); post, at 13 (“After a shooter pulls the
trigger, if he maintains continuous forward pressure on the gun, the
bump stock harnesses the recoil to move the curved lever back and forth
against his finger”).
16                  GARLAND v. CARGILL

                      Opinion of the Court

both engage the trigger and keep it pressed down to con-
tinue shooting. In their view, there is no meaningful differ-
ence between holding down the trigger of a traditional ma-
chinegun and maintaining forward pressure on the front
grip of a semiautomatic rifle with a bump stock. This argu-
ment ignores that Congress defined a machinegun by what
happens “automatically” “by a single function of the trig-
ger.” Simply pressing and holding the trigger down on a
fully automatic rifle is not manual input in addition to a
trigger’s function—it is what causes the trigger to function
in the first place. By contrast, pushing forward on the front
grip of a semiautomatic rifle equipped with a bump stock is
not part of functioning the trigger. After all, pushing on the
front grip will not cause the weapon to fire unless the
shooter also engages the trigger with his other hand. Thus,
while a fully automatic rifle fires multiple rounds “automat-
ically . . . by a single function of the trigger,” a semiauto-
matic rifle equipped with a bump stock can achieve the
same result only by a single function of the trigger and then
some.
   Moreover, a semiautomatic rifle with a bump stock is in-
distinguishable from another weapon that ATF concedes
cannot fire multiple shots “automatically”: the Ithaca Model
37 shotgun. The Model 37 allows the user to “slam fire”—
that is, fire multiple shots by holding down the trigger while
operating the shotgun’s pump action. Each pump ejects the
spent cartridge and loads a new one into the chamber. If
the shooter is holding down the trigger, the new cartridge
will fire as soon as it is loaded. According to ATF, the Model
37 fires more than one shot by a single function of the trig-
ger, but it does not do so “automatically” because the
shooter must manually operate the pump action with his
nontrigger hand. See 

. That logic man-
dates the same result here. Maintaining the proper amount
of forward pressure on the front grip of a bump-stock
equipped rifle is no less additional input than is operating
                      Cite as: 

 (2024)                     17

                           Opinion of the Court

the pump action on the Model 37.8
   ATF responds that a shooter is less physically involved
with operating a bump-stock equipped rifle than operating
the Model 37’s pump action. Once the shooter pulls the ri-
fle’s trigger a single time, the bump stock “harnesses the
firearm’s recoil energy in a continuous back-and-forth cycle
that allows the shooter to attain continuous firing.” 

. But, even if one aspect of a weapon’s operation could
be seen as “automatic,” that would not mean the weapon
“shoots . . . automatically more than one shot . . . by a single
function of the trigger.” §5845(b) (emphasis added). After
all, many weapons have some “automatic” features. For ex-
ample, semiautomatic rifles eject the spent cartridge from
the firearm’s chamber and load a new one in its place with-
out any input from the shooter. See supra, at 10. A semi-
automatic rifle is therefore “automatic” in the general sense
that it performs some operations that would otherwise need
to be completed by hand. But, as all agree, a semiautomatic
rifle cannot fire more than one shot “automatically . . . by a
single function of the trigger” because the shooter must do
more than simply engage the trigger one time. The same is
true of a semiautomatic rifle equipped with a bump stock.
   Thus, even if a semiautomatic rifle could fire more than
one shot by a single function of the trigger, it would not do
so “automatically.”
                          C
  Abandoning the text, ATF and the dissent attempt to
shore up their position by relying on the presumption
——————
  8 The dissent attempts to undermine this analogy by pointing out that

a Model 37 requires manual reloading and therefore cannot qualify as a
machinegun under §5845(b). Post, at 12–13, n. 5. But, that is beside the
point. As ATF itself agrees, the Model 37 is not a machinegun for an-
other, independent reason: It cannot “automatically” fire more than one
shot by a single function of the trigger. See Brief for Petitioners 38. And,
as explained, the reasons why a Model 37 cannot do so apply with equal
force to semiautomatic rifles equipped with bump stocks.
18                  GARLAND v. CARGILL

                      Opinion of the Court

against ineffectiveness. That presumption weighs against
interpretations of a statute that would “rende[r] the law in
a great measure nugatory, and enable offenders to elude its
provisions in the most easy manner.” The Emily, 

 (1824). It is a modest corollary to the com-
monsense proposition “that Congress presumably does not
enact useless laws.” United States v. Castleman, 

 (2014) (Scalia, J., concurring in part and concur-
ring in judgment).
    In ATF’s view, Congress “restricted machineguns be-
cause they eliminate the manual movements that a shooter
would otherwise need to make in order to fire continuously”
at a high rate of fire, as bump stocks do. Brief for Petition-
ers 40. So, ATF reasons, concluding that bump stocks are
lawful “simply because the [trigger] moves back and forth
. . . would exalt artifice above reality and enable evasion of
the federal machinegun ban.” 

 at 41–42 (internal quo-
tation marks omitted). The dissent endorses a similar view.
See post, at 14–17.
    The presumption against ineffectiveness cannot do the
work that ATF and the dissent ask of it. A law is not useless
merely because it draws a line more narrowly than one of
its conceivable statutory purposes might suggest. Inter-
preting §5845(b) to exclude semiautomatic rifles equipped
with bump stocks comes nowhere close to making it useless.
Under our reading, §5845(b) still regulates all traditional
machineguns. The fact that it does not capture other weap-
ons capable of a high rate of fire plainly does not render the
law useless. Moreover, it is difficult to understand how
ATF can plausibly argue otherwise, given that its con-
sistent position for almost a decade in numerous separate
decisions was that §5845(b) does not capture semiautomatic
rifles equipped with bump stocks. See App. 16–68. Curi-
ously, the dissent relegates ATF’s about-face to a footnote,
instead pointing to its classification of other devices. See
post, at 14–17, and n. 6.
                      Cite as: 

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                           Opinion of the Court

   The dissent’s additional argument for applying the pre-
sumption against ineffectiveness fails on its own terms. To
argue that our interpretation makes §5845(b) “far less ef-
fective,” the dissent highlights that a shooter with a bump-
stock-equipped rifle can achieve a rate of fire that rivals tra-
ditional machineguns. Post, at 16. But, the dissent else-
where acknowledges that a shooter can do the same with an
unmodified semiautomatic rifle using the manual bump-fir-
ing technique. See post, at 5. The dissent thus fails to prove
that our reading makes §5845(b) “far less effective,” much
less ineffective (as is required to invoke the presumption).
In any event, Congress could have linked the definition of
“machinegun” to a weapon’s rate of fire, as the dissent
would prefer. But, it instead enacted a statute that turns
on whether a weapon can fire more than one shot “automat-
ically . . . by a single function of the trigger.” §5845(b). And,
“it is never our job to rewrite . . . statutory text under the
banner of speculation about what Congress might have
done.” Henson v. Santander Consumer USA Inc., 

 (2017).9
                            III
  For the foregoing reasons, we affirm the judgment of the
Court of Appeals.
                                            It is so ordered.


——————
  9 The dissent concludes by claiming that our interpretation of §5845(b)

“renders Congress’s clear intent readily evadable.” Post, at 17. And, it
highlights that “[e]very Member of the majority has previously empha-
sized that the best way to respect congressional intent is to adhere to the
ordinary understanding of the terms Congress uses.” Ibid. But, “[w]hen
Congress takes the trouble to define the terms it uses, a court must re-
spect its definitions as virtually conclusive. . . . This Court will not devi-
ate from an express statutory definition merely because it varies from
the term’s ordinary meaning.” Department of Agriculture Rural Devel-
opment Rural Housing Service v. Kirtz, 

, 59 (2024) (internal
quotation marks and alteration omitted) (unanimous opinion).
                 Cite as: 

 (2024)            1

                     ALITO, J., concurring

SUPREME COURT OF THE UNITED STATES
                         _________________

                          No. 22–976
                         _________________


MERRICK B. GARLAND, ATTORNEY GENERAL, ET AL.,
      PETITIONERS v. MICHAEL CARGILL
 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
            APPEALS FOR THE FIFTH CIRCUIT
                        [June 14, 2024]

   JUSTICE ALITO, concurring.
   I join the opinion of the Court because there is simply no
other way to read the statutory language. There can be lit-
tle doubt that the Congress that enacted 

(b) would not have seen any material difference be-
tween a machinegun and a semiautomatic rifle equipped
with a bump stock. But the statutory text is clear, and we
must follow it.
   The horrible shooting spree in Las Vegas in 2017 did not
change the statutory text or its meaning. That event
demonstrated that a semiautomatic rifle with a bump stock
can have the same lethal effect as a machinegun, and it
thus strengthened the case for amending §5845(b). But an
event that highlights the need to amend a law does not it-
self change the law’s meaning.
   There is a simple remedy for the disparate treatment of
bump stocks and machineguns. Congress can amend the
law—and perhaps would have done so already if ATF had
stuck with its earlier interpretation. Now that the situation
is clear, Congress can act.
                  Cite as: 

 (2024)             1

                    SOTOMAYOR, J., dissenting

SUPREME COURT OF THE UNITED STATES
                          _________________

                           No. 22–976
                          _________________


MERRICK B. GARLAND, ATTORNEY GENERAL, ET AL.,
      PETITIONERS v. MICHAEL CARGILL
 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
            APPEALS FOR THE FIFTH CIRCUIT
                         [June 14, 2024]

   JUSTICE SOTOMAYOR, with whom JUSTICE KAGAN and
JUSTICE JACKSON join, dissenting.
   On October 1, 2017, a shooter opened fire from a hotel
room overlooking an outdoor concert in Las Vegas, Nevada,
in what would become the deadliest mass shooting in U. S.
history. Within a matter of minutes, using several hundred
rounds of ammunition, the shooter killed 58 people and
wounded over 500. He did so by affixing bump stocks to
commonly available, semiautomatic rifles. These simple
devices harness a rifle’s recoil energy to slide the rifle back
and forth and repeatedly “bump” the shooter’s stationary
trigger finger, creating rapid fire. All the shooter had to do
was pull the trigger and press the gun forward. The bump
stock did the rest.
   Congress has sharply restricted civilian ownership of ma-
chineguns since 1934. Federal law defines a “machinegun”
as a weapon that can shoot “automatically more than one
shot, without manual reloading, by a single function of the
trigger.” 

(b). Shortly after the Las Vegas
massacre, the Trump administration, with widespread bi-
partisan support, banned bump stocks as machineguns un-
der the statute.
   Today, the Court puts bump stocks back in civilian
hands. To do so, it casts aside Congress’s definition of “ma-
chinegun” and seizes upon one that is inconsistent with the
2                   GARLAND v. CARGILL

                    SOTOMAYOR, J., dissenting

ordinary meaning of the statutory text and unsupported by
context or purpose. When I see a bird that walks like a
duck, swims like a duck, and quacks like a duck, I call that
bird a duck. A bump-stock-equipped semiautomatic rifle
fires “automatically more than one shot, without manual
reloading, by a single function of the trigger.” §5845(b). Be-
cause I, like Congress, call that a machinegun, I respect-
fully dissent.
                                 I
                                 A
   Machineguns were originally developed in the 19th cen-
tury as weapons of war. See J. Ellis, The Social History of
the Machine Gun 21–45 (1986) (Ellis). Smaller and lighter
submachine guns were not commercially available until the
1920s. See Brief for Patrick J. Charles as Amicus Curiae 5
(Charles Brief ). Although these weapons were originally
marketed to law enforcement, they inevitably made it into
the hands of gangsters. See id., at 8–9; Ellis 149–165.
Gangsters like Al Capone used machineguns to rob banks,
ambush the police, and murder rivals. See Ellis 153–154,
157–158. Newspaper headlines across the country flashed
“ ‘Gangsters Use Machine Guns,’ ” “ ‘Machine Gun Used in
Bank Hold-Up,’ ” and “ ‘Machine Gun Thugs Kill Postal Em-
ployee.’ ” Charles Brief 9.
   Congress responded in 1934 by sharply restricting civil-
ian ownership of machineguns. See National Firearms Act
of 1934, §§3–6, 

, 1237–1238. The Senate Re-
port explaining the 1934 Act emphasized that the “gangster
as a law violator must be deprived of his most dangerous
weapon, the machine gun.” S. Rep. No. 1444, 73d Cong., 2d
Sess., 1–2. “[W]hile there is justification for permitting the
citizen to keep a pistol or revolver for his own protec-
tion . . . , there is no reason why anyone except a law officer
should have a machine gun.” 

.
   These early machineguns allowed a shooter to fire in a
                     Cite as: 

 (2024)                   3

                      SOTOMAYOR, J., dissenting

variety of ways. Some would fire continuously with a single
pull of the trigger or push of a button. See Charles Brief 7,
and n. 12 (noting that a Browning M1918 rifle fired eight
rounds “ ‘in a second with one pull of the trigger’ ”); see also
Brief for Petitioners 22 (noting that a Browning M2 fired
with a push of the thumb). Others, such as the famous
Thompson Submachine Gun Caliber .45, or “Tommy Gun,”
would fire continuously only so long as the shooter main-
tained backward pressure on the trigger; a shooter could
still fire single shots by pulling and releasing the trigger
each time. See Test of Thompson Submachine Gun, 69
Army and Navy Register 355 (Apr. 9, 1921) (noting that the
shooter of a Tommy Gun “can fire the contents of the mag-
azine with a single prolonged pull or fire a single shot by
merely releasing the trigger”). The internal mechanisms of
automatic-fire weapons also varied enormously, with many
(such as the Tommy Gun) relying principally on the recoil
energy produced by each bullet’s discharge to effectuate au-
tomatic fire. See, e.g., War Dept., Basic Field Manual:
Thompson Submachine Gun, Caliber .45, M1928A1, p. 1
(1941) (“The Thompson submachine gun . . . is an air-
cooled, recoil-operated, magazine-fed weapon”); W. Smith,
Small Arms of the World: The Basic Manual of Military
Small Arms 165 (1955) (describing Tommy guns as “recoil
operated weapons on the elementary blowback principle”).
  To account for these differences, Congress adopted a def-
inition of “machinegun” that captured “any weapon which
shoots, or is designed to shoot, automatically . . . more than
one shot, without manual reloading, by a single function of
the trigger.” National Firearms Act, 

. That
essential definition still governs today. See 

(b). 1
——————
  1 Congress has twice strengthened the regulation of machineguns over

the years without substantially updating the definition. See Gun Con-
trol Act of 1968, 

 (expanding registration requirements and
strengthening criminal penalties); Firearms Owners’ Protection Act, 100
4                      GARLAND v. CARGILL

                      SOTOMAYOR, J., dissenting

                               B
   The archetypal modern “machinegun” is the military’s
standard-issue M16 assault rifle. With an M16 in auto-
matic mode, the shooter pulls the trigger once to achieve a
fire rate of 700 to 950 rounds per minute. See Dept. of De-
fense, Defense Logistics Agency, Small Arms, https://www.
dla.mil/Disposition-Services/Offers/ Law- Enforcement /
Weapons/. An internal mechanism automates the M16’s
continuous fire, so that all the shooter has to do is keep
backward pressure on the trigger. See Brief for Giffords
Law Center to Prevent Gun Violence et al. as Amici Curiae
9–11 (Giffords Brief ) (discussing internal firing mechanism
of M16). If the shooter stops putting pressure on the trig-
ger, the gun stops firing.
   Semiautomatic weapons are not “machineguns” under
the statute. Take, for instance, an AR–15-style semiauto-
matic assault rifle. To rapidly fire an AR–15, a shooter
must rapidly pull the trigger himself. It is “semi” automatic
because, although the rifle automatically loads a new car-
tridge into the chamber after it is fired, it fires only one shot
each time the shooter pulls the trigger. See 

(a)(29) (2018 ed., Supp. IV).
   To fire an M16 or AR–15 rifle, a person typically holds
the “grip” next to the trigger with his firing hand. He sta-
bilizes the weapon with his other hand on its barrel or
“front grip.” He then raises the weapon so that the butt, or
“stock,” of the gun rests against his shoulder, lines up the
sights to look down the gun, and squeezes the trigger. See
Dept. of the Army, Field Manual 23–9, Rifle Marksmanship
M16A1, M16A2/3, M16A4, and M4 Carbine, Ch. 4, Section
III, p. 4-22 (Sept. 13, 2006) (M16 Field Manual). A regular
person with an AR–15 can achieve a fire rate of around 60
rounds per minute, with one pull of the trigger per second.
——————
Stat. 452–453 (making it a federal crime “ ‘to transfer or possess a ma-
chinegun’ ”).
                   Cite as: 

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                     SOTOMAYOR, J., dissenting

Tr. of Oral Arg. 39. A professional sport shooter can use the
AR–15 to fire at a rate of up to 180 rounds per minute, pull-
ing the trigger three times per second. Giffords Brief 14.
   A shooter can also manually “bump” an AR–15 to in-
crease the rate of fire by using a belt loop or rubber band to
hold his trigger finger in place and harness the recoil from
the first shot to fire the rifle continuously. See 83 Fed. Reg.
66532–66533 (2018). To use a belt loop, he must hold the
rifle low against his hip, put his finger in the trigger guard,
and then loop his finger through a belt loop on his pants to
lock the finger in place. See 

. With his other
hand, he then pushes the rifle forward until his stationary
finger engages the trigger to fire the first shot. See 

The recoil from that shot pushes the rifle violently back-
ward. See 

 If the shooter keeps pressing the rifle for-
ward against the finger in his belt loop, the repeated back-
ward jump of the recoil combined with his forward pressure
allows the rifle to fire continuously. See 

 A shooter
using this method, however, cannot shoot very precisely.
He has neither the advantage of the sights to line up his
shot, nor his shoulder to stabilize the recoil. A shooter can
also use a rubber band or zip tie to tie a finger close to the
trigger. See 

. If the shooter is strong and
skilled enough physically to control the distance and direc-
tion of the rifle’s significant recoil, the rifle will fire contin-
uously.
   A bump stock automates and stabilizes the bump firing
process. It replaces a rifle’s standard stock, which is the
part held against the shoulder. See 

. A bump
stock, unlike a standard stock, allows the rifle’s upper as-
sembly to slide back and forth in the stock. See 

 It also
typically includes a finger rest on which the shooter can
place his finger while shooting, and a “receiver module” that
guides and regulates the weapon’s recoil. 

 To fire a
semiautomatic rifle equipped with a bump stock, the
shooter either pulls the trigger, see ibid., or slides the gun
6                   GARLAND v. CARGILL

                    SOTOMAYOR, J., dissenting

forward in the bump stock, which presses the trigger into
his trigger finger, Cargill v. Barr, 

,
1175 (WD Tex. 2020). As long as the shooter keeps his trig-
ger finger on the finger rest and maintains constant for-
ward pressure on the rifle’s barrel or front grip, the weapon
will fire continuously. See 

. A rifle
equipped with a bump stock can fire at a rate between 400
and 800 rounds per minute. Tr. of Oral Arg. 40.
                               II
    A machinegun does not fire itself. The important ques-
tion under the statute is how a person can fire it. A weapon
is a “machinegun” when a shooter can (1) “by a single func-
tion of the trigger,” (2) shoot “automatically more than one
shot, without manually reloading.” 

(b).
The plain language of that definition refers most obviously
to a rifle like an M16, where a single pull of the trigger pro-
vides continuous fire as long as the shooter maintains back-
ward pressure on the trigger. The definition of “ma-
chinegun” also includes “any part designed and intended
. . . for use in converting a weapon into a machinegun.”

 That language naturally covers devices like bump
stocks, which “conver[t]” semiautomatic rifles so that a sin-
gle pull of the trigger provides continuous fire as long as the
shooter maintains forward pressure on the gun.
    This is not a hard case. All of the textual evidence points
to the same interpretation. A bump-stock-equipped semi-
automatic rifle is a machinegun because (1) with a single
pull of the trigger, a shooter can (2) fire continuous shots
without any human input beyond maintaining forward
pressure. The majority looks to the internal mechanism
that initiates fire, rather than the human act of the
shooter’s initial pull, to hold that a “single function of the
trigger” means a reset of the trigger mechanism. Its inter-
pretation requires six diagrams and an animation to deci-
pher the meaning of the statutory text. See ante, at 8–11,
                  Cite as: 

 (2024)             7

                    SOTOMAYOR, J., dissenting

and n. 5. Then, shifting focus from the internal mechanism
of the gun to the perspective of the shooter, the majority
holds that continuous forward pressure is too much human
input for bump-stock-enabled continuous fire to be “auto-
matic.” See ante, at 14–17.
  The majority’s reading flies in the face of this Court’s
standard tools of statutory interpretation. By casting aside
the statute’s ordinary meaning both at the time of its enact-
ment and today, the majority eviscerates Congress’s regu-
lation of machineguns and enables gun users and manufac-
turers to circumvent federal law.
                                A
   Start with the phrase “single function of the trigger.” All
the tools of statutory interpretation, including dictionary
definitions, evidence of contemporaneous usage, and this
Court’s prior interpretation, point to that phrase meaning
the initiation of the firing sequence by an act of the shooter,
whether via a pull, push, or switch of the firing mechanism.
The majority nevertheless interprets “function of the trig-
ger” as “the mode of action by which the trigger activates
the firing mechanism.” Ante, at 7. Because in a bump-
stock-equipped semiautomatic rifle, the trigger’s internal
mechanism must reset each time a weapon fires, the major-
ity reads each reset as a new “function.” That reading fix-
ates on a firearm’s internal mechanics while ignoring the
human act on the trigger referenced by the statute.
   Consider the relevant dictionary definitions. In 1934,
when Congress passed the National Firearms Act, “func-
tion” meant “the mode of action by which [something] fulfils
its purpose.” 4 Oxford English Dictionary 602 (1933). A
“trigger” meant the “movable catch or lever” that “sets some
force or mechanism in action.” 11 

. The majority
agrees with those definitions. Ante, at 7. It errs, however,
by maintaining a myopic focus on a trigger’s mechanics ra-
ther than on how a shooter uses a trigger to initiate fire.
8                   GARLAND v. CARGILL

                    SOTOMAYOR, J., dissenting

    Nothing about those definitions suggests that “function
of the trigger” means the mechanism by which the trigger
resets mechanically to fire a second shot. See ante, at 8–11
(explaining the interior mechanics of an AR–15 trigger
mechanism), as opposed to the process that a pull of the
trigger on a bump-stock-equipped semiautomatic rifle sets
in motion. The most important “function” of a “trigger” is
what it enables a shooter to do; what “force or mechanism”
it sets “in action.” 11 Oxford English Dictionary, at 357. A
“single function of the trigger” more naturally means a sin-
gle initiation of the firing sequence. Regardless of what is
happening in the internal mechanics of a firearm, if a
shooter must activate the trigger only a single time to initi-
ate a firing sequence that will shoot “automatically more
than one shot,” that firearm is a “machinegun.” §5845(b).
    Evidence of contemporaneous usage overwhelmingly sup-
ports that interpretation. The term “ ‘function of the trig-
ger’ ” was proposed by the president of the National Rifle
Association (NRA) during a hearing on the National Fire-
arms Act before the House. See National Firearms Act:
Hearings on H. R. 9066 before the House Committee on
Ways and Means, 73d Cong., 2d Sess., 38–40 (1934). He
understood the “distinguishing feature of a machine gun [to
be] that by a single pull of the trigger the gun continues to
fire.” Id., at 40. He emphasized that a firearm “which is
capable of firing more than one shot by a single pull of the
trigger, a single function of the trigger, is properly regarded
. . . as a machine gun.” Ibid. Distinguishing a machinegun
from a pistol, the NRA president emphasized that for a pis-
tol “[y]ou must release the trigger and pull it again for the
second shot to be fired.” Id., at 41. He did not say “the
hammer slips off the disconnector just as the square point
of the trigger rises into the notch on the hammer . . .
thereby reset[ting the trigger mechanism] to the original
position.” Ante, at 11. He instead emphasized the action of
                     Cite as: 

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                       SOTOMAYOR, J., dissenting

the shooter, who must repeatedly activate the trigger for
each shot. Predictably, the House and Senate Reports re-
flect the same understanding of the phrase. See H. R. Rep.
No. 1780, 73d Cong., 2d Sess., 2 (1934) (reporting that the
statute “contains the usual definition of machine gun as a
weapon designed to shoot more than one shot without re-
loading and by a single pull of the trigger”); S. Rep. No.
1444, 73d Cong., 2d Sess., 2 (1934) (same).
   The majority cannot disregard these statements as evi-
dence of legislative purpose. 2 They are, along with contem-
poraneous dictionary definitions, some of the best evidence
of contemporaneous understanding. Cf. McDonald v. Chi-
cago, 

 (2010) (THOMAS, J., concurring in
part and concurring in judgment) (“Statements by legisla-
tors can assist . . . to the extent they demonstrate the man-
ner in which the public used or understood a particular
word or phrase”). Indeed, at oral argument, when asked
what evidence there was “that as of 1934, the ordinary un-
derstanding of the phrase ‘function of the trigger’ referred
to the mechanics of the gun rather than . . . the shooter’s
motion,” respondent’s lawyer could not point to a single
piece of evidence that supports the majority’s reading. Tr.
of Oral Arg. 98; see 

 at 98–101. He even agreed that
Congress used the word “function” to ensure that the stat-
ute covered a wide variety of trigger mechanisms, including
both push and pull triggers. 

 at 101–102. In short, the
majority disregards the unrefuted evidence of the text’s or-
dinary and contemporaneous meaning, substituting in-
stead its own understanding of the internal mechanics of an
AR–15 without looking at the actions of the shooter.
   This Court itself has also previously read the definition
of “machinegun” in this exact statute to refer to the action
——————
  2 Of course, “authoritative legislative history can be useful, even when

the meaning can be discerned from the statute’s language, to reinforce
or to confirm a court’s sense of the text.” R. Katzmann, Judging Statutes
35 (2014).
10                      GARLAND v. CARGILL

                       SOTOMAYOR, J., dissenting

of the shooter rather than the firing mechanism. In Staples
v. United States, 

 (1994), the Court noted that
“a weapon that fires repeatedly with a single pull of the trig-
ger” is a machinegun, as opposed to “a weapon that fires
only one shot with each pull of the trigger,” which is (at
most) a semiautomatic firearm. 

 (emphasis
added). A “pull” of the trigger necessarily requires human
input.
   When a shooter initiates the firing sequence on a bump-
stock-equipped semiautomatic rifle, he does so with “a sin-
gle function of the trigger” under that term’s ordinary
meaning. Just as the shooter of an M16 need only pull the
trigger and maintain backward pressure (on the trigger), a
shooter of a bump-stock-equipped AR–15 need only pull the
trigger and maintain forward pressure (on the gun). Both
shooters pull the trigger only once to fire multiple shots.
The only difference is that for an M16, the shooter’s back-
ward pressure makes the rifle fire continuously because of
an internal mechanism: The curved lever of the trigger does
not move. In a bump-stock-equipped AR–15, the mecha-
nism for continuous fire is external: The shooter’s forward
pressure moves the curved lever back and forth against his
stationary trigger finger. Both rifles require only one initial
action (that is, one “single function of the trigger”) from the
shooter combined with continuous pressure to activate con-
tinuous fire. 3
   The majority resists this ordinary understanding of the
term “function of the trigger” with two technical argu-
ments. 4 First, it attempts to contrast the action required to
——————
  3 The majority thinks that this logic should apply just as well to man-

ual bump firing. Ante, at 14. As described supra, at 5, and infra, at 13,
however, bump firing requires much more from the shooter than the sim-
ple forward pressure required to fire a bump-stock-equipped semiauto-
matic rifle.
  4 The majority claims that these arguments explain only “why, even

assuming a semiautomatic rifle equipped with a bump stock could fire
                       Cite as: 

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                         SOTOMAYOR, J., dissenting

fire an M16 from that required to fire a bump-stock-
equipped AR–15. The majority argues that “holding the
trigger down on a fully automatic rifle is not manual input
in addition to a trigger’s function—it is what causes the
trigger to function in the first place” whereas “pushing on
the front grip [of a bump-stock equipped semiautomatic ri-
fle] will not cause the weapon to fire unless the shooter also
engages the trigger with his other hand.” Ante, at 16. The
shooter of a bump-stock-equipped AR–15, however, need
not “pull” the trigger to fire. Instead, he need only place a
finger on the finger rest and push forward on the front grip
or barrel with his other hand. Instead of pulling the trigger,
the forward motion pushes the bump stock into his finger.
   Second, the majority tries to cabin “single function of the
trigger” to a single mechanism for activating continuous
fire. See ante, at 14–15. A shooter can fire a bump-stock-
equipped semiautomatic rifle in two ways. First, he can
choose to fire single shots via distinct pulls of the trigger
without exerting any additional pressure. Second, he can
fire continuously via maintaining constant forward pres-
sure on the barrel or front grip. The majority holds that the
forward pressure cannot constitute a “single function of the
trigger” because a shooter can also fire single shots by pull-
ing the trigger. That logic, however, would also exclude a
Tommy Gun and an M16, the paradigmatic examples of
regulated machineguns in 1934 and today. Both weapons
can fire either automatically or semiautomatically. A
shooter using a Tommy Gun in automatic mode could
——————
more than one shot by a single function of the trigger, it could not do so
‘automatically.’ ” Ante, at 13, n. 6. That is correct, as far as the majority’s
reasoning goes. The majority defines “ ‘single function of the trigger’ ” as
a reset of a rifle’s internal trigger mechanism. Ante, at 11. A more accu-
rate definition is the human action required to initiate the firing se-
quence. Supra, at 7–10. The majority’s argument for why “something
more than a ‘single function of the trigger’ is required to fire multiple
shots,” ante, at 15, is therefore relevant to both its discussion of “auto-
matically” and my discussion of “single function of the trigger.”
12                      GARLAND v. CARGILL

                       SOTOMAYOR, J., dissenting

choose to fire single shots with distinct pulls of the trigger,
or continuous shots by maintaining constant backward
pressure on the trigger. See supra, at 3. An M16 user can
toggle the weapon from semiautomatic mode, which allows
only one shot per pull of the trigger, to automatic mode,
which enables continuous fire. See M16 Field Manual, Sec-
tion III, p. 4-8. In 1934 as now, there is no commonsense
difference between a firearm where a shooter must hold
down a trigger or flip a switch to initiate rapid fire and one
where a shooter must push on the front grip or barrel to do
the same.
   The majority’s logic simply does not overcome the over-
whelming textual and contextual evidence that “single
function of the trigger” means a single action by the shooter
to initiate a firing sequence, including pulling a trigger and
pushing forward on a bump-stock-equipped semiautomatic
rifle.
                              B
  Next, consider what makes a machinegun “automatic.” A
bump-stock-equipped semiautomatic rifle is a “ma-
chinegun” because with a “single function of the trigger” it
“shoot[s], automatically more than one shot, without man-
ual reloading.” §5845(b). Put simply, the bump stock auto-
mates the process of firing more than one shot.
  Before automatic weapons, a person who wanted to fire
multiple shots from a firearm had to do two things after
pulling the trigger the first time: (1) he had to reload the
gun; and (2) he had to pull the trigger again. A semiauto-
matic weapon like an AR–15 already automates the first
process. The bump stock automates the second. 5 In a fully
——————
  5 The majority attempts to analogize a bump stock to the Model 37

shotgun, which allows the user to “fire multiple shots by holding down
the trigger while operating the shotgun’s pump action.” Ante, at 16. The
Model 37 automates the second process (i.e., pulling the trigger for each
shot), as long as the shooter maintains pressure on the trigger. Unlike a
                     Cite as: 

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                       SOTOMAYOR, J., dissenting

automatic rifle like an M16, that automation is internal.
After a shooter pulls the trigger, if he maintains continuous
backward pressure on the trigger, the curved lever itself
will not move. Instead, an internal mechanism allows con-
tinuous fire. On a bump-stock-equipped semiautomatic ri-
fle, the automation is external. After a shooter pulls the
trigger, if he maintains continuous forward pressure on the
gun, the bump stock harnesses the recoil to move the curved
lever back and forth against his finger. That external au-
tomated motion creates continuous fire.
   When a shooter “bump” fires a semiautomatic weapon
without a bump stock, he must control several things using
his own strength and skill: (1) the backward recoil of each
shot, including both the direction in which the rifle moves
and how far it moves when recoiling; (2) the trigger finger,
by maintaining a stationary position with a loose enough
hold on the trigger that the rapidly moving gun will hit his
finger each time; and (3) the forward motion of the rifle af-
ter it recoils backward. A bump stock automates those pro-
cesses. The replacement stock controls the direction and
distance of the recoil, and the finger rest obviates the need
to maintain a stationary finger position. All a shooter must
do is rest his finger and press forward on the front grip or
barrel for the rifle to fire continuously.
   The majority nevertheless concludes that a bump-stock-
equipped semiautomatic rifle requires too much human in-
put to fire “automatic[ally]” because it requires the “proper
amount of forward pressure on the front grip” to maintain
continuous fire. Ante, at 16. “Automati[c],” however, does
not mean zero human input. An M16 requires the shooter
to exert the “proper amount of [backward] pressure on the”

——————
semiautomatic rifle, however, the Model 37 does not automate the first,
as the shooter “must manually operate the pump action with his nontrig-
ger hand” to “ejec[t ] the spent cartridge and loa[d ] a new one into the
chamber.” 

14                  GARLAND v. CARGILL

                   SOTOMAYOR, J., dissenting

trigger to maintain continuous fire. 

 So, too, a ma-
chinegun that requires a user to hold down a button. Mak-
ers of automatic weapons may require continuous human
input for safety purposes; an accidental trigger pull that ac-
tivates rapid fire is less harmful if it does not require af-
firmative human action to stop. Requiring continuous pres-
sure for continuous fire, however, does not prevent a
firearm from “shoot[ing], automatically more than one
shot.” §5845(b).
                               C
   This Court has repeatedly avoided interpretations of a
statute that would facilitate its ready “evasion” or “enable
offenders to elude its provisions in the most easy manner.”
The Emily, 

, 389–390 (1824); see also
Abramski v. United States, 

, 181–182, 185
(2014) (declining to read a gun statute in a way that would
permit ready “evasion,” “defeat the point” of the law, or
“easily bypass the scheme”). Justice Scalia called this in-
terpretive principle the “presumption against ineffective-
ness.” A. Scalia & B. Garner, Reading Law: The Interpre-
tation of Legal Texts 63 (2012). The majority arrogates
Congress’s policymaking role to itself by allowing bump-
stock users to circumvent Congress’s ban on weapons that
shoot rapidly via a single action of the shooter.
  “The presumption against ineffectiveness ensures that a
text’s manifest purpose is furthered, not hindered.” 

Before machineguns, a shooter could fire a gun only as fast
as his finger could pull the trigger. Congress sought to re-
strict the civilian use of machineguns because they elimi-
nated the need for a person rapidly to pull the trigger him-
self to fire continuously. A bump stock serves that function.
Even a skilled sport shooter can fire an AR–15 at a rate of
only 180 rounds per minute by rapidly pulling the trigger.
Anyone shooting a bump-stock-equipped AR–15 can fire at
a rate between 400 and 800 rounds per minute with a single
                      Cite as: 

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                        SOTOMAYOR, J., dissenting

pull of the trigger.
   Moreover, bump stocks are not the only devices that
transform semiautomatic rifles into weapons capable of
rapid fire with a single function of the trigger. Recognizing
the creativity of gun owners and manufacturers, Congress
wrote a statute “loaded with anticircumvention devices.”
Tr. of Oral Arg. 68. The definition of “machinegun” cap-
tures “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.” §5845(b). Not “more than four, five, or six shots,”
not “single pull” or “single push” of the trigger.” Following
that definition, the Bureau of Alcohol, Tobacco, Firearms
and Explosives (ATF) has reasonably classified many trans-
formative devices other than bump stocks as “ma-
chinegun[s].” 6 For instance, ATF has long classified “forced
reset triggers” as machineguns. See Brief for Petitioners
28. A forced reset trigger includes a device that forces the
trigger back downward after the shooter’s initial pull, re-
peatedly pushing the curved lever against the shooter’s sta-
tionary trigger finger. See ibid. To a shooter, a semiauto-
matic rifle equipped with a forced reset trigger feels much
like an M16. He must pull the trigger only once and then
maintain pressure to achieve continuous fire. See ibid.
   Gun owners themselves also have built motorized devices
that will repeatedly pull a semiautomatic firearm’s curved
——————
  6 The majority emphasizes that ATF previously took the position that

certain bump-stock devices were not “machinegun[s]” under the statute.
See ante, at 3, 19. ATF, however, has repeatedly classified other devices
that modify semiautomatic rifles by allowing a single activation of the
shooter to automate repeat fire as machineguns. See, e.g., 

, n. 4 (referencing ATF classifications of trigger reset devices);
Akins v. United States, 

, 200–201 (CA11 2009) (per cu-
riam) (upholding classification of Akins Accelerator, a spring-operated
bump stock); United States v. Camp, 

 (CA5 2003) (up-
holding classification of fishing reel attached to a rifle trigger that, upon
activation, repeatedly operated the curved lever of the rifle).
16                      GARLAND v. CARGILL

                       SOTOMAYOR, J., dissenting

lever to enable continuous fire. ATF has classified such de-
vices as “machinegun[s]” since 1982. See Record 1077. In
2003, the Fifth Circuit held that such a contraption quali-
fied as a “machinegun” under the statute. See United
States v. Camp, 

. An owner of a semiau-
tomatic rifle had placed a fishing reel inside the weapon’s
trigger guard. 

. When he pulled a switch behind
the original trigger, the switch supplied power to a motor
connected to the fishing reel. 

 The motor caused the
reel to rotate, and that rotation manipulated the curved
lever, causing it to fire in rapid succession. 

 ATF in
2017 also classified as a “machinegun” a wearable glove
that a shooter could activate to initiate a mechanized piston
moving back and forth, repeatedly pulling and releasing a
semiautomatic rifle’s curved lever. See Record 1074–1076. 7
   The majority tosses aside the presumption against inef-
fectiveness, claiming that its interpretation only “draws a
line more narrowly than one of [Congress’s] conceivable
statutory purposes might suggest” because the statute still
regulates “all traditional machineguns” like M16s. Ante, at
18. Congress’s ban on M16s, however, is far less effective if
a shooter can instead purchase a bump stock or construct a
device that enables his AR–15 to fire at the same rate. Even
bump-stock manufacturers recognize that they are exploit-
ing a loophole, with one bragging on its website “Bumpfire
Stocks are the closest you can get to full auto and still
be legal.” Midsouth Shooters, BUMPFIRE SYSTEMS,
https://www.midsouthshooterssupply.com/b/bumpfire-

——————
   7 Respondent does not today challenge ATF’s classification of these de-

vices as “machinegun[s].” His lawyer noted at oral argument, however,
that “forced reset triggers” would be part of a category of “harder cases”
where “there may be a question as to what exactly the trigger is and then
how does that trigger function.” Tr. of Oral Arg. 82. That ambiguity
stems from the majority’s loophole for weapons that require multiple me-
chanical actions to fire continuously, even when a shooter initiates that
fire with a single human action.
                  Cite as: 

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                    SOTOMAYOR, J., dissenting

systems. The majority creates a definition of the statute
that bans only “traditional” machineguns, even though its
definition renders Congress’s clear intent readily evadable.
   Every Member of the majority has previously emphasized
that the best way to respect congressional intent is to ad-
here to the ordinary understanding of the terms Congress
uses. See, e.g., Jam v. International Finance Corp., 

 (2019) (ROBERTS, C. J., for the Court) (“ ‘[T]he
legislative purpose is expressed by the ordinary meaning of
the words used’ ”); Gross v. FBL Financial Services, Inc.,

 (2009) (THOMAS, J., for the Court) (“ ‘Stat-
utory construction must begin with the language employed
by Congress and the assumption that the ordinary meaning
of that language accurately expresses the legislative pur-
pose’ ”); Wall v. Kholi, 

 (2011) (ALITO, J.,
for the Court) (“ ‘We give the words of a statute their ordi-
nary, contemporary, common meaning, absent an indica-
tion Congress intended them to bear some different im-
port’ ”); BP p.l.c. v. Mayor and City Council of Baltimore,

 (2021) (GORSUCH, J., for the Court)
(“When called on to interpret a statute, this Court generally
seeks to discern and apply the ordinary meaning of its
terms at the time of their adoption”); Sackett v. EPA, 

 (2023) (KAVANAUGH, J., concurring in
judgment) (reasoning that departing from “all indications
of ordinary meaning” will “create regulatory uncertainty for
the Federal Government . . . and regulated parties”); Bar-
tenwerfer v. Buckley, 

, 77, 83 (2023) (BARRETT,
J., for the Court) (declining to “artificially narrow ordinary
meaning” to “second-guess [Congress’s] judgment”). Today,
the majority forgets that principle and substitutes its own
view of what constitutes a “machinegun” for Congress’s.
                      *     *    *
  Congress’s definition of “machinegun” encompasses
bump stocks just as naturally as M16s. Just like a person
18                 GARLAND v. CARGILL

                  SOTOMAYOR, J., dissenting

can shoot “automatically more than one shot” with an M16
through a “single function of the trigger” if he maintains
continuous backward pressure on the trigger, he can do the
same with a bump-stock-equipped semiautomatic rifle if he
maintains forward pressure on the gun. §5845(b). Today’s
decision to reject that ordinary understanding will have
deadly consequences. The majority’s artificially narrow
definition hamstrings the Government’s efforts to keep ma-
chineguns from gunmen like the Las Vegas shooter. I re-
spectfully dissent.