Not sure of the question, but you can't legally put a barrel less than 16 on any firearm with a shoulder stock or which will end up less than 25" long, without an OK from BATF. In this case, the barrel length can include a muzzle brake if it is welded to the barrel and not readily removable, but that would still be a 16" barrel for practical purposes.
It is OK to make a short-barrel rifle (SBR) but you need to file the form and pay the tax ($200).
Jim