Roy Rogers' horse is content as a gunman might be (7-5)

I believe the answer is:

trigger-happy

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'a gunman might be' is the definition.
I can't judge whether this definition defines the answer.

'roy rogers' horse is content' is the wordplay.
'roy rogers' horse' becomes 'trigger' (I've seen this before).
'is content' becomes 'happy' (associated in meaning).
'trigger'+'happy'='TRIGGER-HAPPY'

'as' is the link.

Can you help me to learn more?

(Other definitions for trigger-happy that I've seen before include "inclined to recklessness" , "enjoying shooting" , "Over-ready to shoot" , "Over-enthusiastic with a gun" , "Irresponsible with firearms" .)

I've seen this clue in The Irish Independent.

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