Why would you want to put a muzzle break on a M&P10? Not very much recoil there. Just practice more and you won't need it. Or trade in the gun for something that you can handle. Only thing a muzzle break is good for is holding pencils on your desk. Ever seen a muzzle brake on a 458 Lott or 505 Gibbs? Of course not! Those are bolt action guns that are very likely to be in rather dangerous situations where a fast second shot is needed. And they have serious recoil. If muzzle brakes are not used on those, why on earth would you think you need one on a 308?