Document ID: ./input/supremecourt_opinions/opinions/23pdf/22-976_e29g.pdf
Page Number: 7.0

Cite as:  602 U. S. ____ (2024) 

3 

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 

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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.