I got some TrailBoss powder and I loaded 50 rounds. I will have to go to the range next weekend. Ill post up my results. Im going to see if the rounds are stable and if so, then I will try them with the suppressor.
I loaded most with 4.0gr of trailboss and I loaded a few with 3.6 gr. On another forum, a few said the 4.0 grs breaks the sound barrier, and a few had good luck with 3.6 gr. COL is 2.200 with Sierra 55gr GameKing bullets.
Here is a youtube video of a person shooting subsonic .223 loads.
http://www.youtube.com/watch?v=xiUqB-LCHhA