If you've spent any real time running a .300 Blackout build, you already know it's one of the most versatile cartridges on the market — equally at home punching paper with subsonic loads through a suppressor or reaching out with supersonic rounds for hunting and range work. But that versatility comes with a catch: subsonic and supersonic .300 BLK ammunition generate wildly different amounts of gas pressure, and a fixed gas system simply can't handle both well. That's where an adjustable ga …