Smooth metal? Unacceptable (7)

I believe the answer is:

ironout

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'smooth' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'metal? unacceptable' is the wordplay.
'metal?' becomes 'iron' (iron is a metal).
'unacceptable' becomes 'out' (out can mean incorrect or inappropriate).
'iron'+'out'='IRONOUT'

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I've seen this clue in The Daily Express.

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