For most people case head expansion compared to a known load.
If you are shooting a wildcat things get tougher.
Does the action open as normal? Or is it hard to open?
Does the fired case extract freely?
If you index a cartridge before firing, can you, after firing the round, remove then re-insert it and close the action to make the saftey interlock work properly? And while closing the action normaly, not snapping it shut.
Can the case head expansion be compared to the parent case?
I know these methods don't tell you what the pressures are, but these are the signs of high to too high pressure.