Maybe you have a short chamber? When you FL sized, did you cam over? In other words, you set your seater down touching your ram, and then turn another 1/4 turn? Most do not turn down enough. Also did you check to see if they needed trimmed?

You most likely needed to cam over more. On alot of FL sizers, pulling the expander ball thru will actually pull the neck up some. Thats the reason, most of the time, I use a universal deprimer, and deprime, and then size without any expander ball, and then push the expander ball thru, in a later step, not pull it thru. I did alot of this to control neck runout, but it didn't really help much.