Burst of fire from Pole, maybe after swapping the middle round (5)

I believe the answer is:

salvo

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'burst of fire' is the definition.
(I've seen this in another clue)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for salvo that I've seen before include "Fusillade, volley" , "Broadside" , "Rapid simultaneous shooting" , "Ceremonial round of gunfire" , "Unusual excuse" .)

I've seen this clue in The Times.

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