Emptied firearm and its contents thus missing antelope (3)
I believe the answer is:
gnu
'antelope' is the definition.
(gnu is a kind of antelope)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for gnu that I've seen before include "Large heavy antelope" , "Wildebeest" , "Literally wild beast" , "Strange gun for an antelope" , "Large African antelope" .)