RE: the most exotic cartridge ever
Check our Cartridges of the World, or Dunleavey's handbok of Cartridge Conversions. Wouldn't consider .22K Hornet or .357 Herret as rare, the Lazeroni is a production cartridge, even if it is limited production. .338/06 Barrels and reamers are available from several sources, if you reload, it is no big deal to load for, and not terribly expensive.