Barrels are regulated and you need paper to send them to the US. For instance I can not send a barrel direct to Briley for choke work. They use a company in Ontario to ship I believe.
https://help.cbp.gov/app/answers/det...eTk4TUxUZW4%3D
One small cut out:
An unlicensed person may obtain a permit to import sporting ammunition (excluding armor-piercing, tracer, or incendiary ammunition) and firearm parts (
other than frames, receivers, firearm barrels, or barreled actions) without engaging the services of a Federal Firearms License (FFL), provided the items are for personal use and not for resale. Generally, ATF cannot issue a permit authorizing the importation of firearms barrels for non-sporting or surplus military firearms.