300 Blackout ammo was developed by Advanced Armament Corporation and Remington Defense in 2010 and standardized by the Sporting Arms and Ammunition Manufacturers Institute (SAAMI) in 2011, the 300 AAC Blackout (also known as 300 BLK or 7.63x35mm) is a relatively young cartridge, but one that is rapidly gaining in popularity.
The 300 BLK was developed around a long list of design parameters intended to allow the use of .30 caliber projectiles in the AR/M4 platform. Chief among them, the cartridge had to feed reliably from standard 30 round magazines and utilize their full capacity, which previous attempts with the 7.62x39 cartridge (used in the AK-47) failed to do. Other requirements included the ability to operate suppressed or unsuppressed in a short, lightweight configuration.
The propellants used in 300 BLK cartridges tend to be much faster burning than typical rifle powders, meaning the 300 BLK is well suited to pistol-length gas systems and suffers relatively little in the way of velocity when fired from short barrels. This makes the 300 BLK an ideal choice for AR-style pistols or short-barreled rifles.
The cartridge uses a shortened 221 Fireball or .223 Remington case, shortened to 35mm with the new case mouth necked down to .308 caliber. Bullet weights for the 300 BLK range from 110 grain to 250grain, with lighter projectiles suited to maximum velocity while the heavier bullets are used for subsonic work and maintain high energy despite limited velocity.
Ballistically, the 300 BLK performs much like the 7.62x39mm cartridge, with a shorter effective range than 5.56x45mm NATO, but with more kinetic energy than the latter. Because of these characteristics, the 300 BLK is well suited to close range combat and for hunters wishing to use the AR platform.