I have been shooting 300 whispers for 12 years and the new 300 blackout for a year. The cases are so close they are basically the same. I have been loading subsonic for the whisper/300 Blackout forever and having a ball shooting supressed subsonic rounds. I bought a 16 inch barrell .308 Winchester that is at the smith's getting threaded for my Suppressor. I bought some 170 gr round nose 30/30 bullets and a can of Trail Boss that I feel will work nice for subsonic loads. Does anyone have experience with Trail Boss and .308 Winchchesters?