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