Re: 300 whisper advantage over 308 sub sonic???
for a bolt gun I would run subsonic 308 with Trailboss. I have had very good luck with it in a Rem 700, a ruger in 243, and a M1A in 308. The M1a would not cycle though.
I have been running 1"-1.25" in a Rem. 700 SPS, HS PSS take off stock, MK4...