Point being, some compensators and brakes will direct a lot of gas to the sides and up. So goes the noise, and they get much louder to the shooter and those beside them.
The linears push it all out front. It's the best compromise short of a suppressor. Look at the decibel table here: http://www.ar15performance.com/muzzle_devices?b=1
I bought a Black River Tactical for my 6.8, the ITS 4X4 tunable was reputedly the better but is now no longer offered that way. Maybe it crossed the line. The BATF is strict that any reduction makes it a suppressor. In MO, they are legal to possess and use hunting, haven't found the Vltor Volks for $400 like promised at SHOT 2010, and haven't applied to make one, either. But, I could, paperwork in order, and spend less than $30. Even at $3000, you'd still hear the action cycling just like charging the weapon, they don't really silence a gun anyway.
ALL firearms in a caliber appropriate for deer hunting will ring your ears, no matter what. Even a .22. or fireworks will do it, no sense tossing the 6.8 for what 20+ grains of gunpowder will do regardless. If you're hunting, it's just one or two shots. I've gotten more hearing damage from a day's worth of non-lethal projectile training, not wearing plugs is a collectively abusive choice I've grown to regret.
Sorry, had to wave off those mosquitoes again. They sure disappear fast, my wife swears I'm just hearing something.