A gun barrel cooler for cooling a firearm, such as an automatic, semi-automatic, bolt action or lever action rifle that includes a centrifugal fan blower with an intake to which ambient barrel coolant air is discharged from the blower where the air flows through a conduit that preferably is a flexible hose, through a coupling used to couple the hose to a barrel coolant discharge nozzle, and out the nozzle into the barrel of the gun desired to be cooled. The nozzle is three dimensionally shaped to substantially conform to the firing chamber of the gun to provide better sealing during cooling. A preferred nozzle is an empty cartridge case of substantially the same caliber as the gun to be cooled that is removably attached to the coupler thereby enabling cartridge cases of different calibers to be used to cool guns of different calibers.