TexasCHLforum.com

Be aware that if you merely purchase an upper with a 14.5" barrel - perfectly legal on one of the pistol versions of the AR being sold - and all you have is an AR rifle, the BATmen may assert that you're in "constructive possession" of an SBR even if it's never been attached to your S&W M&P15.

Unless it's registered as an SBR, the minimum required barrel length is indeed 16" measured from the breech face to the end of the muzzle, and yes, a permanently attached muzzle brake or flash hider counts when it comes to "making length."