Missile contains large bang (4)
I believe the answer is:
slam
'bang' is the definition.
(I've seen this before)
'missile contains large' is the wordplay.
'missile' becomes 'sam' (abbreviation for surface-to-air missile).
'contains' is an insertion indicator.
'large' becomes 'l'.
'sam' placed around 'l' is 'SLAM'.
(Other definitions for slam that I've seen before include "Hit hard" , "Shut (door) with force" , "Ambitious contract" , "Winning all (or all but one) of the tricks in bridge" , "Close noisily" .)