There are things you own that are not legal to own or use in Europe. The use of the 4457 is down stream of finding out what the law says about scopes, types of scopes, legal use of scopes, traveling with scopes, and if there might be differences between what the locals are permitted versus visitors. The 4457 doesn’t mean Jack to a European Customs agent, it only allows you to document to US authorities that you left with a piece of property, and returned with same.
What makes you positive that bringing a scope is actually permitted for a foreign national where he is going? Have you done it?
I’m still curious as to why you would believe, from reading his post, that there was a rifle going with him.
Best,
Ted