When you say split cases, do they look similar to the attached picture? These were some of the first rounds from the wifes PPK/S, Sellier & Belloit brand, which the cases were on the thin walled side of standard. They would initially get cut while still in the mag by the housing around the firing pin which is semi exposed with a slot. The edges of the slot were very sharp, I performed some stoning work of the slots and the problem disappeared. Some additional stoning and polishing in other areas and the pistol works flawless. The wife will not part with it. Good luck with yours.