Since us commoners can't take a barrel and cut it down anything less than ~18", but a newly manufactured (non-semi-auto) barrel can be any length so long as the new rifle meets OAL requirements, I wonder what type of markings are required on a barrel blank? I assume somewhere they list calibre, length, and a manufacturers mark? I read in another thread that any smith listed as a firearms manufacturer can make a barrel, and I wonder if that would include modifying an existing barrel to less than 18", or if it's new manufacture only.