Like so many others on this thread, I recommend the John Masen double muzzlebrake/flash hider. It does an excellent job of damping barrel harmonics, and produces a dramatic increase in accuracy.
Note that mine wasn't a totally tight fit (others have reported this problem as well). It requires a small shim of brass, aluminum or even a strip cut from a tin can to make the brake fit snugly.
Note that mine wasn't a totally tight fit (others have reported this problem as well). It requires a small shim of brass, aluminum or even a strip cut from a tin can to make the brake fit snugly.