Gun may be spoilt (6)
I believe the answer is:
pistol
'gun' is the definition.
(I know that pistol is a type of firearm)
'may be spoilt' is the wordplay.
'may' is an anagram indicator (I've seen 'might' mean this (I've seen this in other clues)).
'spoilt' anagrammed gives 'PISTOL'.
(Other definitions for pistol that I've seen before include "Spoilt these guns" , "Rectangular" , "A small hand-gun" , "Piece" , "Officer's side-arm" .)