Long-barrelled weapon (5)
I believe the answer is:
rifle
'long-barrelled weapon' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rifle that I've seen before include "Steal and carry off - firearm" , "Winchester" , "loot in sack" , "Ransack - firearm" , "Gun; sack" .)