Quote Originally Posted by kbaltrusch View Post
I have AR platform rifles in .223 and .308, as well as suppressors to go with them. First question I have is will the rifle cycle with a subsonic round? Second question is what kind of loads to use? I read in a American Rifleman magazine a few years ago, where you could use something like 9 grains of a pistol powder to achieve this. But I don't remember which powder and if that was for a .223 or .308. Any recipes for a subsonic load in either of those calibers?
I don’t really have any loads in either so I can’t really answer the question you asked, but would like to see if you have come up with a suitable answer to your question. I have 30cal suppressors. Why not use your 223 lower and a 300blackout upper? You would still be sending a 30cal projectile down range at subsonic speeds getting very similar ballistics to the subsonic 308 and use your suppressor. There’s no changing springs or need for adjustable gas blocks and will cycle the action without hesitation. I have a sbr that I frequently switch between a 12” 223 upper and a 8” 300blackout upper. I’m thinking of adding a 18” 6.5 Grendal upper to the current pair to use as a “kit” type of setup. 300blackout for close range quiet work, 223 for medium distance work and 6.5 for anything that stretches out to about the most of my abilities.