AAC 300 Blackout Cartridge. 300 BO. Using the new state of the art MK 319 MOD 0 bullet, velocity is 2180 feet per second using a Remington 700 16” 1/8” twist barrel. SUB MOA Capable. Description of the 308 round. The open-tipped rounds until now have been available only to Special Operations Command troops. The first 200,000 7.62 Special Operations Science and Technology rounds are already downrange with Marine Expeditionary Brigade-Afghanistan. SOCOM developed the new rounds for use with the Special Operations Force Combat Assault Rifle, or SCAR, which needed a more accurate bullet because its short barrel, at 13.8 inches, is less than an inch shorter than the M4 carbine’s. Using an open-tip match round design common with some sniper ammunition, SOST rounds are designed to be “barrier blind,” meaning they stay on target better than existing M855 rounds after penetrating windshields, car doors and other objects. Gunn Ammo has incorporated this special purpose bullet into the 300 BlackOut. During our testing, it penetrated 19” of solid wet news paper and the bullet recovered expanded from.30 to .56 in diameter.