Brass cracking just behind shoulder

[amafrank]

I normally anneal the big stuff like the .338, .50cal and the 20mm but I've never annealed the 30-.221. I've got some cases that have been fired at least 12 times since conversion from .223 to the 30 and never had a case split for any reason. Even the cases I was using to test the high velocity stuff has been fired 7 or 8 times and still no splits...I have had some primer pockets open up though.
Maybe the problem with your splitting is due to a large chamber and a small die. ..

Frank