I was going to a lot of trouble to size .30-'06 bases down to the correct size for 9X56MS, when I happened to pick up a piece of unfired Remington .35 Whelen brass from my loading bench and measured the base. Lo and behold, it was already the right size. Brass problem solved.

I am sure you are aware that Hornady makes .268" diameter bullets for the 6.5 Carcano, which are the correct size for most 6.5 MS barrels. Be careful, though. I have a Greek MS which had been rebarrelled, and the new barrel is .264". Fortunately a cartridge loaded with a .268" bullet will not chamber in it. I am thinking of adopting a color code system like the Germans have with their 8mm cartridges, whereby they paint the primers on the "S" (.323") diameter cartridges black.