Have done .223 to 7mm TCU and 30`06 to .35 Whelen before Remington brought it out as a factory option. Anealing the necks will help but is`nt necessary. Start with new or cleaned once fired brass and dip the necks in powdered graphite after lubeing. Never split a case neck this way except when I tryed some nickel plated .223.
Good luck and have fun. I had a Savage 99 in that chambering once, a very fine and underated cartarage.