After many attempts, and all of them very expensive, to actually have properly head stamped brass in my various B&M cartridges, I finally gave up. I have spent close to $10,000 now, with several different brass makers, and have so little brass that it almost don't matter. Most of the brass was not able to handle the same pressures that the parent case handles, another problem..........
In the end, I decided to have the Barrels Engraved with the parent cartridge and the actual cartridge....
Example; 458 B&M/300 Remington Ultra Mag...... or similar........... This covers all bases for those uneducated Customs Officers you just might run into somewhere around the Planet. Today, I might reverse and have the parent cartridge engraved first, followed by the actual......... So now, you have 300 Rem Ultra on the brass, and on the barrel, hard to question that, and I promise you, that Customs guy is not going to know the difference between 300 and 458....... I have traveled the world like this multiple times over and never had an issue.... as stated above, it is rare that any checks head stamp and barrel markings to begin with. I actually only had one time that this happened and it was in Namibia once. After a bit of explaining, it was sorted out.
Much easier to have the barrel engraved than to attempt to get brass.......