Oil company's importing gems and guns (6)
I believe the answer is:
biceps
'guns' is the definition.
(I've seen this in another clue)
'oil company's importing gems' is the wordplay.
'oil company's' becomes 'bps' (I can't justify this - if you can you should give a lot more credence to this answer).
'importing' is an insertion indicator.
'gems' becomes 'ice' (ice is slang for diamonds).
'bps' enclosing 'ice' is 'BICEPS'.
'and' is the link.
Can you help me to learn more?
(Other definitions for biceps that I've seen before include "Upper-arm muscle" , "Muscle that flexes the forearm" , "Arm workers" , "Weightlifters use them" , "Arm muscles" .)