What is 300 AAC Blackout?

According to its inventors at the Advanced Armament Corporation, 300 AAC Blackout is “full power 123-grain ammunition [for the AR platform] that matches the ballistics of the 7.62x39mm AK, with 37% more energy than 5.56mm M855, and 9% more than 6.8 SPC TAP 110.” In fact, “from a 9 inch barrel, the 300BLK has more muzzle energy than 5.56mm M855 from a 16 inch barrel. When 300 BLK is used in a 16 inch barrel, it has 23% more energy than 5.56mm M855 from a 16 inch barrel – with much higher-mass projectiles for a more dramatic effect on the target.” Or . . . “choose subsonic cartridges for optimal use with a sound suppressor – 220 grain Sierra OTM (open-tip match) bullets vastly outperforms a 9mm MP5-SD in penetration and long range accuracy.” There’s a lot more, but I partied pretty hard last night . . . Anyway, I like big and slow (e.g. Russian 9x39mm). Just sayin’.