I've loaded the 7mm Remington for 40 years and never had a case, primer, or pressure problem until the case was discarded after about 5-7 maximum loads. Per Ken Waters, as soon as I saw primer flattening, or more than .005 increase in head measurement, I would back down .5 grain. The primer pocket "prolapse" was the usual culprit. I was taught to full size the case when new; then, place a nickel between the shell holder and the die. The belted cases head space on the belt, so any additional working of the brass accelerated insipient head separation.