Short bits of barrel are not a barrel without being attached to a firearm.
Exactly. Until machined to accept a cartridge and /or fit to a receiver, they are not actual gun barrels. Similar to an unfinished Ar-15 receiver. If you were found with one that you created because you took a saw to barrel or parted one off from a barrel you were chambering, you would have a legitimate reason for its creation, and not one associated with making an attempt at anything illegal.