How short can I go on a 308 bolt gun barrel to shoot only subsonic loads with a YHM Phantom stainless. Maybe permanently attached. 400 yards max range.
If you were to permanently attach the Phantom, you could do an 8" barrel. The Phantom is 8.5" long. If you were to go that short, I would run a 7 twist barrel. That way you can stabilize the 240 SMK's. Also, Trailboss is a great powder choice.