Sack might be full of such weaponry? (9)

I believe the answer is:

firepower

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'full of such weaponry?' is the definition.
I can't tell whether this defines the answer.

'sack might' is the wordplay.
'sack' becomes 'fire' (both can mean to dismiss from a job).
'might' becomes 'power' (being mighty).
'fire'+'power'='FIREPOWER'

'be' is the link.

Can you help me to learn more?

(Another definition for firepower that I've seen is " Strength available".)

I've seen this clue in The Irish Times.

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