As far as I know, a part is not a complete firearm. I wouldn't be transporting a barrel that was used in a murder or anything, but to be on the safe side, if you are driving it somewhere, put it in a lockable case in the trunk.
Oops...I should have read more accurately. For international, I would get something in writing from the other country. I know Mexico gives a stiff jail sentence for one round of ammunition.
[This message has been edited by PreserveFreedom (edited October 18, 2000).]