One of the tests I performed at the Wester Powders piezo lab dealt with the "accuracy" of the long-time pressure-signs still used by many handloaders. I handloaded some rounds for three different rifle cartridges using such signs as flattened primers, case-head expansion, sticky extraction, and ejector-hole marks on the case heads.
Then I loaded up new cases of the same brand with all three loads and we tested 'em in the Miles City lab. It turned out that one load just about spot-on, another was way under SAAMI pressure, and the third was way over SAAMI pressure.
Ran some other tests in their lab back then, and it turned out that most "pressure signs" except primer flatness don't show up until around 70,000 PSI average maximum pressure--which is 5000 PSI more than SAAMI allows for any cartridge. Primer flatness, however, can occur even with pressures in the 50,000 PSI range, usually due to a little more headspace than SAAMI specs allow.
