Thanks, I lost my link to that list.
Ok.. some people are confused about CUP & CIP.
But I am not one of them.
There are three main types of chamber pressure instruments; crusher, strain gauge, and piezoelectric transducer. I haven't heard of a major industrial user of strain gauges, that seems to be a hobby or small company approach.
There have been others, the Powley P-Max operated on recoil, of all things, and there was a device which imbedded a sensitive insert in the cartridge head itself, to be read on the fired case, out of the gun, by an external meter, no gun modifications required. Both were short lived in the market.
There was a shop with an axial gauge like old British practice, you could send in your own barrel and ammo to know the actual characteristics you were getting, with no worry about an ammo company's PV barrel differing from a conventional rifle's.
There are multiple standard setting organizations, SAAMI in the US, CIP has apparently taken over all the previously independent European proof houses and their national proof laws. Then there are Army and NATO methods and standards.
So you can find a lot of different numbers representing the chamber pressure of one particular load.
Looking in Lyman 49 I see both CUP and psi. In fact for some cartridges like 7mm Remington Magnum, I see both in the same table.
Frex, a 168 gr Sierra + 64 gr IMR 4831 = 2915 fps @ 60,500 psi. But 65 gr H4831 = 2971 fps @ 52,000 CUP.
These are both maximum loads for those particular powders by the method tested, the actual numbers don't matter, they were not arrived at the same way.
So what? I can't measure them anyhow.
But the powder charges do matter. I will not likely exceed the maximum and might even stop short if I get better accuracy or "pressure signs" short of the maximum.
Then you get into "load shopping." My old Sierra manual stops at 62.2 gr IMR 4831 for that bullet, but goes up a smidgen to 65.6 gr of H4831.
So which is "right?"
How about those old manuals with the Good Stuff? A lot of their loads were reached by eyeballing brass and primers and maybe by stopping when they had factory velocity or a little more, just like you can.