smokepole,
General Hatcher mentioned the unreliability of primer appearance as a pressure indicator in HATCHER'S NOTEBOOK, first published in 1947. He knew a thing or two about pressures in rifle ammo, since he was one of the U.S. military's top ordnance officers for many years, the reason he was Technical Editor of AMERICAN RIFLEMAN after his retirement.
Unfortunately, he didn't go into any detail about why primer appearance is so unreliable, apparently thinking the reasons were obvious--such as varying thickness in primer cups, added to variations in headspace. I've got a collection of old issues of AMERICAN RIFLEMAN and am slowly going through them, among other things looking for details to his statement about primer appearance. Will post them if I find any, though among many Campfire members the opinions of dead guys don't matter, because their post-count is so low.
