We hunted with STWs for years back when it was a pure wildcat, great cartridge but finicky. We had to make cases out of 300 Weatherby back then. Those long belted cases get head separations really easy so even bumping the dogmatic .002in can eventually lead to it. Other long belted cases suffer the same fate, ie. 300 Weatherby, 300 WIN, 7mm REM etc.