Carrying a gun did make it bulge (7)
I believe the answer is:
distend
'bulge' is the definition.
(I've seen this before)
'carrying a gun did make' is the wordplay.
'carrying' is an insertion indicator.
'a gun' becomes 'sten' (British sub-machine gun).
'did make' becomes 'did' (doing is a kind of making).
'sten' put inside 'did' is 'DISTEND'.
'it' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for distend that I've seen before include "Swell by pressure from within" , "Bloat" , "balloon" , "Swell with internal pressure" , "blow up" .)