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Page Number: 20.0

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 83 Fed. Reg. 66534.  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