The NBRSA does allow a muzzle brake for Light Gun and Heavy Gun in 600 & 1000 yard competition.

I do use a muzzle brake on my Hunter Class rifle to help me deal with a shoulder injury from a motorcycle accident. I also have muzzle brakes on all my hunting rifles. If the brakes are banned, it has been nice knowing you all.

I did developed a blast shield this last winter that really works as attested to by shooters at several ranges whom I shot next to this spring and summer(it is a plastic cone). The politics of the shield situation were such that I was not allowed to use it at the Nationals.