If an individual powder and projectile mostly for subsonic masses turns out to operate for .three hundred Blackout that might be excellent. If it turned out to that CFE 223 could fill that position that could be the best of all worlds. You'll need to tweak subsonic handloads according to https://dallasgzmzp.onesmablog.com/getting-my-300-blackout-bullets-for-reloading-to-work-77998156