Barrel length is measured from breachface to end of the barrel. If the muzzle device is permanently attached (pinned and welded) it is considered part of the barrel. My setup you are referencing is 16.1” from breachface to end of muzzle device BUT I have not pinned and welded it so it is considered an SBR because the barrel is only 14.5” long. As soon as I pin it the barrel will be considered 16.1” and non SBR. Currently that upper is riding on a registered SBR lower though so it is legal.