Second case of pistols for arms contractor? (7)
I believe the answer is:
triceps
'contractor?' is the definition.
(I know that triceps is a muscle organ)
'second case of pistols' is the wordplay.
'second' becomes 'trice' (both can mean a very short amount of time).
'case of' suggests removing the centre (outsides of).
'pistols' with its centre removed is 'ps'.
'trice'+'ps'='TRICEPS'
'for arms' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for triceps that I've seen before include "Three-headed muscle" , "Green citrus fruit" , "Extensor muscle" , "One stretches out an arm!" , "Source of uplifting strength" .)