Miller, if you hadn't started by apparently being unfamiliar with SAAMI terminology--which I copied directly from their data--you wouldn't have been confused. SAAMI, being primarily concerned with maximum pressures (proof or service), starts out by listing Maximum Average Pressure. Which is, as far as I know, the number to which reloaders pay attention since they don't want to exceed the Max Avg Pressure for the gauge in question as determined by SAAMI. Reloaders have no idea of the "total pressure" and have no way of measuring it. The best they can do is look at a reloading manual or website and the pressure stipulated in that manual or website. If they're not worried about the pressure stipulated in the book, then they proceed to reload. It's not really rocket science.
Referring back to Mr. Roster's article: Many of us are aware of the fact that the CIP standard service pressure (10,730 psi) is lower than the SAAMI service pressure (11,500). So if we're dealing with CIP guns proofed to the CIP standard, we shoot for a lower number. Likewise, the SAAMI standard was lower for short chambered American shotguns than it is for modern guns, which gives us yet another reason to seek out loads that one may not necessarily define as "low pressure", but are certainly lower pressure than the 11,500 psi we might get if we were to touch off a modern American factory 12ga shell.
