First... welcome to the forum!

Well, to start with, the 220gr RN Hornady over 40.0 grains of IMR-4350 is about as close as you're going to get to the original .30 Army round.  Split/cracked necks is nothing new in reloading for 30-40... we've all experienced it.  However, all is not lost. 

1. I can't stress this enough:  Anneal your case necks!  I use my LEE Trimmer collet and chuck them up in the drill.  I spin the case while heating the case neck until it changes color (and no more).  I then drop them into a metal bowel to air cool.  Some people drop them into water, but I believe this to be unnecessary. 
2.  Neck Size Only!  Keep your brass separated to a specific rifle and once they're fire-formed, neck size the brass only, which will prevent unnecessary working of the brass.  I use LEE Pacesetter dies and back my sizing die out one full turn. 

Follow these two rules, and your brass should last a very long time.  I'm well over twenty reloads on some of my brass, and still occasionally get cracks... but they'll certainly last far longer!