The .300 AAC Blackout cartridges were developed by Advanced Armament Corporation (AAC) for use in the M4 carbine to achieve ballistics similar to the 7.62x39mm supersonic cartridge, and to offer a subsonic yet powerful cartridge for the AR15 platform as an alternative to the MP5SD 9mm, all while utilizing a standard (STANAG) magazine. Our BarnauL .300BLK, available now, is a 145-grain supersonic cartridge with a polymer-coated steel case. This is the most affordable .300BLK ammunition on the market today. A .300BLK subsonic cartridge is a heavy, lower-velocity round perfect for pairing with a suppressor. Using subsonic cartridges with a suppressor helps to eliminate the "crack" that is inherent with supersonic cartridges, reducing noise levels down to a safer volume. *CASE OF 200 ROUNDS