Rifle filler (4)
I believe the answer is:
ammo
'rifle filler' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ammo that I've seen before include "eg Bullets, shells" , "Bullets, say, in short" , "Bullets, shells, etc. (abbr.)" , "Bullets and bombs, etc (abbr)" , "What's fired from a gun (abbr)" .)