The Initial run of 500 S&W Mag cases was built to use large pistol primer per Smith & Wesson and Cor-bon specifications. On July 28, 2003, Smith & Wesson and Cor-bon changed specification of primer pocket to be large rifle. Rifle primers are same diameter as pistol except they are approximately .006" taller. This was done to prevent primer from being pierced by firing pin when loaded with max loads and heavy bullets (bullets over 400 grains).