I have as many manuals and books on reloading I can get my hands on.

Just remember if a specific firearm is listed then a strain gauge is glued to the barrel to get the pressure reading.

And if a universal receiver and pressure test barrel is listed then a direct pressure reading was taken.

The difference being if a strain gauge is used it must be calibrated with a cartridge of a known pressure. Meaning cartridges tested in a universal receiver using a pressure transducer. And pressure test barrels have a minimum diameter bore to generate the highest possible pressure.

This explains why the loading data can vary so much between firearms and test methods.

And no matter what data is used, making workup loads and started at the suggested start loads will teach you a great deal about your firearms and components used.