This gun is obviously a repeater (6)

I believe the answer is:

pompom

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'this gun' is the definition.
(pompom is a kind of gun)

I can't explain the remainder of the clue.

(Other definitions for pompom that I've seen before include "Anti-aircraft cannon - woolly ball" , "Decorative ball of tufted wool" , "Woolly decoration" , "Anti-aircraft weapon" , "Cheerleader's ball of material" .)

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