You didn't specify barrel length but either way, IMHO no a muzzle break isn't needed. Both supersonic and subsonic loads use slow pistol powders which are pretty much all burned off in the first 9" or so, this means minimal flash. As for recoil, subs runs about 25k or so chamber pressure and supers about 55K. Even though the bullets are heavier than .223/5.56 the pressures are less so felt recoil is about the same, at least on my 8.3", 11", and 16" uppers.