under pressure is just as likely to cause catastrophic failure as over pressure, and primers alone don't tell you much about pressures, if you have a flat primer alone you don't know what your shooting, (this came from a ballistic tech at Sierra) if for that firearm you have a flattened primer along with ejector wipes, chances are your over pressure, if you have case Head expansion over .001" you are definitely over pressure for that firearm loaded with those components.
RR