I'm not sure that the "permanent fixture" is relavent for post-ban rifles that have the legal 16" barrel in place. It is a muzzle brake, not a "flash suppressor". I think (and someone correct me if I'm wrong) that the only time the brake has to be attached permanently is when it is necessary to be a part of the barrel to make it 16" in length. That is, to attach a 4.5" brake to a 11.5" barrel to make it legal.