move the gas block further up the barrel. venting much more forward means less gas to bleed if it's too much. also, using more of the lower power gas than using a little of the high power is easier on the bolt and will result in less force = less noise. the action should then vent downward, away from the shooter's ears or other persons. the longer barrel will also burn more powder, which makes it easier to suppress at the muzzle. add an adjustable piston to comfortably cycle the action. the longer barrel would keep it lethal at longer ranges too.
but alas, that would require a complete redesign of the rifle into some kind of downward ejecting rifle of some sort. despite this, i firmly believe that adhering to the antiques of old is still the right path.