The butts indicate how far the bullets go (8,5)
I believe the answer is:
shooting range
'the butts indicate how far' is the definition.
I can't tell whether this defines the answer.
'bullets go' is the wordplay.
'bullets' becomes 'shooting' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'go' becomes 'range' (ranging is a kind of going).
'shooting'+'range'='SHOOTING-RANGE'
'the' is the link.
Can you help me to learn more?
(Other definitions for shooting range that I've seen before include "Source of reports" , "Gun practice area" , "where folk fire off guns" , "Place for gun or rifle practice" , "target area" .)