I've seen uppers, barrels, and rifles before that are 14.5" with a pinned 1.5" flash hider that are considered 16" barrels because the flash hider is permanently attached for a total length of 16". My question is, if I were to do this myself, would the gun technically be illegal after it's been cut but before the flash hider's been pinned? If so, would I have to send it somewhere and get that done?