I had two hang fires (scary!) when I first started loading for my 500 Jeffery before I switched to Federal 215 primers and kept my loads with a grain or two of max. I'm shooting 570g TSX's at 2300 fps. No problems since. I had been shooting 535g Woodleighs (no fault to the bullet) at 2000 fps, too slow. These big cases want a hot primer and high load density.