The diameter of a primer pocket grows about 2X as fast as the OD of the case head.
Different brands in various cartridges may react differently. For example, Remington nickel-plated brass used in a Ruger No.1 in .45-70 would handle 60,000 to 63,000 psi (as measured by a US lab) for at least 10 firings with no discernible primer pocket expansion (using WLRM primers). They were then thrown out. Federal nickel-plated .45-70 brass couldn't begin to handle that psi before primer pockets were loose enough to not hold new primers.
The report from the head ballistician to me was, "You have just reinvented the .458 Winchester Magnum, what was the recoil like?" From a 24" test barrel their average MV was 2096 fps from the 500gr Hornady Int. RN. A rep from Ruger told me, "The Ruger No.1 in .45-70 is just as strong as a Ruger No.1 in .458 Winchester Magnum.
The word from that well known ballistician was "That load is safe in your Ruger No.1". No one in that lab had any previous idea that using the right powder, primer, case and bullet, that a .45-70 case could safely be used at those specs in a rifle capable of easily digesting it. I was getting an average of 2015 fps. My "new" Ruger in .45-70 had the throat lengthened nearly twenty years ago for even better performance by seating bullets "long".
There are opinions, and then there are facts.
Bob
www.bigbores.ca
