Re: Muzzle brakes affect on accuracy?
First of all welcome to this site. You will find much good info around here.
To answer your question directly, adding a muzzle brake can change the way your barrel vibrates. This may or may not change the way your load performs. In any event, if you are getting good groups now, they most likely can be had after a brake is added. It is possible a slight change in powder weight may be needed to repeat the tight groups.
Brakes also add to your shooting comfort. Comfort = accuracy. A brake can also add better accuracy to your rifle by diverting the muzzle blast away from the bullet upon its exit.
Hope that helps some.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.