Not knowing about part of a gun - a war experience! (7)
I believe the answer is:
unaware
'not knowing' is the definition.
(I've seen this before)
'part of a gun a war experience' is the wordplay.
'part of' says the answer is hidden in the clue.
'UNAWARE' is hidden within 'gun a war experience'.
'about' acts as a link.
(Other definitions for unaware that I've seen before include "Not knowing (of a situation or fact)" , "Not realising" , "Heedless" , "Not having knowledge or realisation" , "In the dark" .)