.300 AAC Blackout
The .300 AAC Blackout (designated as the 300 BLK by the SAAMI and 300 AAC Blackout by the C.I.P.), also known as 7.62×35mm, is an intermediate cartridge developed in the United States by Advanced Armament Corporation (AAC) for use in the M4 carbine. The cartridge yields increased performance in shorter barrels and effective subsonic performance for suppressor use when compared to 5.56mm NATO. The 300 AAC Blackout utilizes standard 5.56mm NATO magazines and components with the exception of the barrel.