On the U.S. end of things 22 CFR Ch. 1 Part 123 covers the ITAR, Customs and State Dept. requirements for exporting arms. Part 123.16 has a list of exemptions and one of those exemptions is pre-1898 Original and Reproduction/Replica firearms.

On the BATFE end of things 27 CFR has a similarly word set of exemption for Pre-1898 Original and Reproduction/Replica Firearms.

There are a few hoops to jump through(paperwork mostly) but shipping Muzzleloaders and Pre-1898 Cartridge Rifles(even greater than .50 Caliber) isn't a problem so long as the country you are shipping to isn't on the U.S. restricted list.

Now the Gov't BS and Paper trail and Taxes(Gov't Bribes) on the receiving countries end might be a whole other story depending on where the Muzzleloader is going.

I've shipped a couple of Muzzleloaders over seas in the last couple of years and other than a few declarations that had to be made on the paperwork the whole process was fairly straight forward.

Cost of shipping on the other hand, especially with insurance coverage for full replacement value will just about choke a horse.

Colin