A silencer (suppressor) is not legally defined by appearance but by the fact that it reduces the sound level. A brake is not a suppressor, or vice versa, but a device that does both would legally be a suppressor, not a brake.
Yeah, but then you get into the matter of silencer parts. If I make a flash suppressor/muzzle brake that is a 6" long version of some of the breaks that direct the noise/gas out and to the rear (something like this but a little wider and 6" long: http://www.ebay.com/itm/M44-Muzzle-B...tem231417f964;
and then thread the end of the brake, would that be a silencer part or a muzzle brake? By itself, it does nothing to reduce sound. Screw a can on it and it, or just wrap it in some insulation and it could reduce sound.