Slamfire;
You said splits, did you mean cracks around the case at the body/ base juncture or cracks lenghtwise on the case?
The lenghtwise cracks could be from hardened brass, annealing might slow or stop that.
Did you measure a fired case to see how big the body is after firing?
The body should be .420 + -", if much larger, you may make a sleeve of very thin brass ,at least .15-.2 " long press it on the case until it is seated just ahead of the extractor groove , fire form and the case will expand without stressing the head/ body joint.
I do this in making .30-30 cases for use in my .303 Savage '99.
Don