Re: Performance Loss with Muzzle brake ?
There should be little if any change in energy or trajectory if you don't change the actual bore length. There should be no reduction in accuracy if the muzzle brake is properly centered, has proper clearances, and has symmetrical ports. It may still shoot fine with carefully designed asymmetric ports such as in a combined brake and compensator. Point of aim will most likely change from adding a brake, but accuracy is shot to shot repeatability.
The added weight on the barrel is likely to change the barrel harmonics a little requiring tweaking hand loads if they had been optimized without the brake. Factory ammo may shoot a little better or worse for the same reason.
There are also human aspects. Reducing felt recoil can help accuracy, Increasing muzzle blast can hurt accuracy. Both are the result of anticipating the effect, consciously or not. Which may have more effect is hard to guess.