Royal Artillery battalion ultimately fires rifles (8)
I believe the answer is:
ransacks
'rifles' is the definition.
('ransack' can be a synonym of 'rifle')
'royal artillery battalion ultimately fires' is the wordplay.
'royal artillery' becomes 'RA' (abbreviation).
'ultimately' says to take the final letters.
'fires' becomes 'sacks' ('sack' can be a synonym of 'fire').
The final letter of 'battalion' is 'n'.
'ra'+'n'+'sacks'='RANSACKS'
(Other definitions for ransacks that I've seen before include "Rifles" , "Plunders, loots" , "Takes as spoils" , "Plunders and pillages" , "Pillages or searches roughly" .)