There doesn't appear to be a subsonic option in .300 blackout beyond tracer rounds.. Which i wouldn't use in a stealth op for obvious reasons. The other .300 rounds all deliver the distinctive crack when you are shot at with it. It's a shame because the RHS AS VAL is my only subsonic rifle option with any penetrating power atm, and i'd like to use a SCAR AAC or honeybadger. 7.62x51 subsonic is crap and 5.56 is even worse