Discharge rifle (4)

I believe the answer is:

sack

I believe this clue is a double definition.

'discharge' is the first definition.
(I know that discharge can be written as sack)

'rifle' is the second definition.
(I've seen this before)

(Other definitions for sack that I've seen before include "Fire the old drink?" , "Get rid of" , "Large hessian bag" , "Discharge" , "Fire - plunder and destroy" .)

I've seen this clue in The Irish Independent, The Times and The Telegraph.

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