Legality
Muzzle brakes were ruled legal by the ATF in the United States a short time after the now defunct Federal Assault Weapons Ban went into effect in 1994. These muzzle components were legal as long as they were a permanent fixture of the barrel and were legal to attach to a threaded barrel, so long as they were welded in place on certain firearms (high temperature silver solder also sufficed). However, flash suppressors and barrel shrouds were seen as 'military' features, and were on the list of features that, provided enough features were present, defined the rifle as illegal, if manufactured after the effective date of the ban. As such, a flash suppressor, modified by users to operate as a muzzle brake, were not in compliance. The Federal laws governing this expired in 2004.
In some African jurisdictions where big game hunting is commonplace, rifles (typically firing powerful loads) equipped with muzzle brakes are banned due to hearing damage hazard to scouts and guides without hearing protection.
Read more about this topic: Muzzle Brake