both barrels

In reference to discharging both barrels of a double-barrelled shotgun simultaneously rather than one at a time.

both barrels pl (plural only)

1. (informal, figuratively) The maximum damage that a weapon can deliver.

   to give someone both barrels

   to let someone have both barrels

   to hit someone with both barrels

• “give someone both barrels” (US) / “give someone both barrels” (UK) in Macmillan English Dictionary.
• “let someone have both barrels” in the Cambridge English Dictionary, Cambridge: Cambridge University Press.