Damaged, but OK in a gun (6)
I believe the answer is:
broken
'damaged' is the definition.
(associated in meaning)
'ok in a gun' is the wordplay.
'in' indicates putting letters inside.
'a gun' becomes 'Bren' (Bren is an example).
'ok' inserted inside 'bren' is 'BROKEN'.
'but' is the link.
(Other definitions for broken that I've seen before include "Defective" , "If it's not ..., don't fix it" , "Busted, damaged" , "no longer working?" , "faulty" .)