Please read before threading barrel!!
By Canadian legal definition, the barrel is measured from the bolt face to the end of the rifling. By this definition, the AR180B barrel is 18 1/4 inches long, and prohibited. How ever, as the muzzle brak is an integral part of the barrel, this put the AR180B barrel over 18.5 inches (the legal limit for a centre fire semi-auto)
If you thread the barrel, cutting the barrel back to the end of the rifling will be too short! you must leave some of the muzzle brake extension intact when threading the barrel to maintain the minimum length of 18.5 inches. the barrel length does not include the flash suppressor.
Make sure your gunsmith knows this!