Old gun's redesigned square hub (9)

I believe the answer is:

harquebus

I'm a little stuck... Click here to teach me more about this clue!

'old gun's' is the definition.
'harquebus' can be an answer for 'gun's' (harquebus is a kind of gun). I'm unsure of the 'old' bit.

'redesigned square hub' is the wordplay.
'redesigned' is an anagram indicator.
'square'+'hub'='squarehub'
'squarehub' anagrammed gives 'HARQUEBUS'.

Can you help me to learn more?

(Other definitions for harquebus that I've seen before include "Weapon" , "Gun" .)

I've seen this clue in the Sydney Morning Herald.

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