Part of a barrel to break into we hear (6)

I believe the answer is:

breech

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'part of a barrel' is the definition.
('breech' is part of 'barrel')

I don't understand the rest of the clue.

(Other definitions for breech that I've seen before include "Back end of a gun barrel" , "Describing a delivery in which the baby is inverted" , "Back part of a gun barrel" , "Prat" , "(Half of) lower garment" .)

I've seen this clue in The Globe and Mail.

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