Soften up minute inclusion in submachine gun (7)
I believe the answer is:
sweeten
'soften up' is the definition.
(I've seen this before)
'minute inclusion in submachine gun' is the wordplay.
'minute inclusion' becomes 'wee' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'submachine gun' becomes 'sten' (I've seen this in another clue).
'wee' going into 'sten' is 'SWEETEN'.
Can you help me to learn more?
(Other definitions for sweeten that I've seen before include "Appease" , "Make more agreeable or acceptable" , "Make more palatable" , "Add sugar etc" , "Make sugary or saccharine" .)