Cover revolting case of firearm (9)

I believe the answer is:

upholster

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'cover' is the definition.
(I've seen this before)

'revolting case of firearm' is the wordplay.
'revolting' becomes 'up' (I've seen this in other clues).
'case of firearm' becomes 'holster' (I can't explain this - if you can you should believe this answer much more).
'up'+'holster'='UPHOLSTER'

Can you help me to learn more?

(Other definitions for upholster that I've seen before include "restore the throne?" , "Provide furnishings" , "Pack seats" , "Furnish with padding" , "Cover furniture" .)

I've seen this clue in The Independent.

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