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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