Mountains frequented by riflemen (5)
I believe the answer is:
range
'mountains' is the definition.
(range of mountains)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for range that I've seen before include "Enclosed kitchen fireplace" , "Extent; line of mountains" , "Scope, extent" , "Aga or mountain, perhaps?" , "Cooking appliance" .)