Ive posed this question before to IGF. The response I got was it was never submitted to BATFE for classification as a muzzle break. If you buy one, just keep the receipt that says "muzzlebreak" and you will be 1/2 protected from future trouble. That is, you didn't have a "criminal intent" when you installed it. FWIWhttp://www.investmentgradefirearms.com/images/For Sale/hkbrakefront.jpg
Is IGFs muzzle break a flash hider or compensator ... to the ATF that is...