Here's where shotgun barrel importing is covered.
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.
