Originally Posted by W.K.Shuridys
It's a metal tube with no rifling, no threads, and is unlikely to ever be identified as something remotely firearm-related unless declared so on the package. Even then, barrels are not controlled articles here and are not subject to import restrictions unless they're prohibited handgun barrels (which this is most obviously not).
I'd order it from the States without hesitation.
I agree. This should be looked at by customs as nothing more than a copper tube.