Gun; ransack (5)
I believe the answer is:
rifle
I believe this clue is a double definition.
'gun' is the first definition.
(I know that rifle is a type of firearm)
'ransack' is the second definition.
(rifle can mean to ransack or rob)
(Other definitions for rifle that I've seen before include "Winchester" , "An arm" , "Rummage" , "Search and rob for army weapon" , "Gun; plunder" .)