Managed to discharge rifle (7)
I believe the answer is:
ransack
'rifle' is the definition.
('ransack' can be a synonym of 'rifle')
'managed to discharge' is the wordplay.
'managed' becomes 'ran' (I've seen this before).
'to discharge' becomes 'sack' ('sack' can be a synonym of 'discharge').
'ran'+'sack'='RANSACK'
(Other definitions for ransack that I've seen before include "Search (a place) thoroughly" , "Plunder or turn upside down in search" , "Loot or search thoroughly" , "Search thoroughly and roughly" , "Plunder; search ruthlessly" .)