A bit instinctive, getting a gun (13)

I believe the answer is:

semiautomatic

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'a bit instinctive getting a gun' is the definition.
I can't tell whether this definition defines the answer.

'instinctive getting a gun' is the wordplay.
'instinctive getting' becomes 'semi' (I can't explain this - if you can you should give a lot more credence to this answer).
'a gun' becomes 'automatic' (automatic is a kind of gun).
'semi'+'automatic'='SEMIAUTOMATIC'

Can you help me to learn more?

(Other definitions for semiautomatic that I've seen before include "Type of firearm" , "Like some firearms" .)

I've seen this clue in The Daily Express.

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