That's my bad, I deleted a dot in your variable, use :

Code:
alias 870 {
  inc %870
  inc %870. $+ $1
  say takes his 870 shotgun, put inside several shells, aim against  $1 and fires..  (Shoots with his 870: %870 ,Shoots against $1: $eval($($+(%,870.,$1),2) $+ )
}

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