The 300 Blackout (300 BLK) was designed by Remington/AAC to create a reliable, compact .30 caliber round for the AR platform that uses a standard bolt and magazine. 300 Blackout is optimized for suppressed fire with heavy bullet subsonic loads but can also be used with supersonic ammunition when extra range is needed. The twist rate will work well for subsonic and supersonic loadings alike and there is typically no need for an adjustable gas block when switching back and forth between the two loadings. All these specifications come together to create a round that is great for home defense, law enforcement / military use, as well as hunting.
The 300 AAC Blackout delivers ballistic performance comparable to 7.62×39, yet possesses a base diameter that optimizes functionality in an AR-type platform. It is cross-compatible with 223 Rem/5.56×45 magazines. The 300 Blackout’s .30 caliber bullet can be made especially long, and as the result may weigh up to 220 grains — quadruple the weight of the typical 223 Rem round’s. So heavy a bullet conveys a subsonic muzzle velocity and correspondingly softer report. Converting an AR-15 to fire 300 Blackout is as simple as swapping its barrel. Although functionally identical to the 300 Whisper, the 300 AAC Blackout is its own SAAMI standardized cartridge.