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Call of Duty Wiki
The subject of this article appears in Call of Duty: Modern Warfare (2019) The subject of this article appears in Call of Duty: Warzone

"Custom barrel with a slight length increase and polygonal rifling for increased muzzle velocity and improved range. Adds little additional weight."
— In-game description

The 13.1" First Responder is a barrel attachment featured in Call of Duty: Modern Warfare and Call of Duty: Warzone. It is uniquely available to the Uzi submachine gun.