Here's a thumbnail guide to SAAMI max average pressure for most of the chamberings in common use. Make a copy of this for your reference. If you have additions, please add them below. Thanks. Safety first!
There is absolutely no correlation between CUP and PSI. None at all. People have tried and failed. It just doesn't work, there's too many variables with case volume and barrel volume. The reason you see CUP listings is because the cartridge in question is not popular enough, does not generate enough sales to justify the expense of testing with a piezo-electric setup. Each cartridge tested on piezo-electric equipment costs quite a lot, to where a lab won't do it if not worth the cost or laboratory time. DO NOT, repeat DO NOT try to interpret PSI pressure by looking at the CUP reading, you may get in trouble. Trust lab info that has been tested.There is no 1:1 correlation between PSI and CUP...
However, the SAAMI publications often cite both measurement values.
For each specific cartridge, the ratio varies.
For example, the 243 Winchester is 60,000 PSI and 52,000 CUP.
The PSI/CUP ratio is 1.153846
For this cartridge, those interested in converting CUP to PSI can multiply CUP * 1.153846 to find PSI.
This is approximate, but probably much closer than a SWAG.
SAAMI does not publish both numbers for all cartridges.
No one can answer that because no one agrees. Loading Manual maximums for Trapdoors:so this chart implies 28,000# for .45/70. Is that within reasonable operating pressures for the last group of trapdoors? I believe the 1886 models?