Weird Problem Loading Rifle Cases

Check the diameter of the bullets against the diameter of your expander ball - sounds like it's not expanding enough.

If you didn't chamfer the mouth of the cases, that will do it. Boat tailed bullets seat fine without chamfering but flat based bullets don't.

I've never had any problems with seating a regular flat based bullet.
I'd also suspect that your bullets are bigger than your expander.

Id say clean the die and expander ball for one. then are you lubing the inside and outside or just the outside. Usually i like to only lube the outside. On the inside a bit of graphite with a qtip does great. I had that problem once. Now i changed the way i reload and make sure the expander ball is tight so it does not wonder. Other wise your case neck will be all wacked.

May also want to do as others said. chamfer the case mouths slightly. then mic out the bullets to make sure they are consistant

Is this fairly low use brass or high mileage stuff? That would account for neck splits.

Buckling at the shoulder is usually caused (in my experience) by excessive crimp.