Go through in search for gun (5)
I believe the answer is:
rifle
I believe this is a double definition.
'go through in search' is the first definition.
(I've seen this before)
'for gun' is the second definition.
(rifle is a kind of gun)
(Other definitions for rifle that I've seen before include "Plunder - ransack" , "Flier (anag.)" , "Firearm - plunder" , "Gun; thoroughly search" , "Gun; sack" .)