.300 AAC Blackout Subsonic

The .300 AAC Blackout (7.62×35mm) is one of the most popular and well-suited calibers for subsonic applications, designed from the outset to excel in suppressed, short-barrel, and subsonic performance. Developed specifically to function reliably in AR-15 platforms with standard 5.56mm bolts and magazines, the .300 BLK has become a top choice for tactical and hunting use where noise reduction and close-range stopping power are critical.

Subsonic .300 Blackout loads typically feature heavy bullets in the 190–240 grain range, with 220gr bullets like the Sierra MatchKing or Hornady Sub-X being particularly common. These projectiles deliver excellent energy retention and terminal performance at subsonic velocities, usually around 1,010–1,050 fps. The cartridge’s compact case size and efficient powder burn allow for reliable cycling in semi-automatic rifles when paired with a suppressor and the appropriate gas system (typically pistol-length).

Popular powders for subsonic .300 BLK include Hodgdon H110, IMR 4227, Accurate 1680, and Vihtavuori N110. These powders offer good case fill and consistent pressure curves, minimizing the risk of pressure spikes or incomplete ignition. A 1:8 or 1:7 twist rate is recommended for stabilizing heavier subsonic bullets, especially in short barrels.

Key considerations for subsonic .300 BLK include ensuring reliable cycling, suppressor optimization, and maintaining accuracy through careful load development. The caliber’s unique ability to switch seamlessly between full-power supersonic and stealthy subsonic loads without changing platforms gives it unmatched versatility. For subsonic use, it remains one of the most efficient and effective calibers available today.