I believe things have changed a lot in 14 years. Here, in Denmark, we do not need a permit for a silencer, and we have European weapon pass for our rifles. If we travel to or through Germany by car with a silencer without permit (and they apparently vary from state to state) we risk confiscation of rifle plus a huge fine. I would not dare going in or out of an international airport without whatever permits required. Can you do that in the US, I think not and we see the US as being much more lax when it comes to weapons than Europe?
Here in Denmark it would surely also be a no-go without the permits, which I don't even know how to obtain, but probably something like in Germany. Just importing a barrel (basically a steel pipe) is a major undertaking that can only be transported by specialised shippers.
My best bet would be to listen to Charlie64