It’s a gun, kid! Put back those gems! (7)
I believe the answer is:
garnets
'gems' is the definition.
(garnet is a kind of gem)
'it's a gun kid put back' is the wordplay.
'it's a gun' becomes 'sten' (British sub-machine gun).
'kid' becomes 'rag' (I've seen this in other clues).
'put back' shows that the letters should be reversed in order.
'sten'+'rag'='stenrag'
'stenrag' in reverse letter order is 'GARNETS'.
'those' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for garnets that I've seen before include "Strange turn of the gemstones" , "Stones" .)