When the 500 mag came out, the first cases were made for large pistol primers. When it was determined that they could not efficiently ignite the large powder charge, they changed the spec to large rifle primers. This required them to make the primer pockets deeper to accommodate the thicker large rifle primers. Those cases are marked on the head stamp with an "R" for large rifle primer. If you seat a large rifle primer in one of those early cases, it will be about .001 to .002 proud. DeWalt is correct. Large rifle primers are thicker than large pistol primers. But don't believe us. Grab your mic and measure a few.