Well Ed, you could always send some rounds to Tom Armbrust for pressure testing. But the factory loads you buy today may have different components or different powders the next time you buy them. So if you find some factory load that is low enough pressure, it might be a good idea to stock up before they change. The major ammo makers do not tell us pressures, or notify us that they are switching powder, primers, etc. They just sell shells that are within SAAMI specs.
The only other options are to purchase ammo from suppliers like RST or B&P who specialize in low pressure ammo for vintage guns, or to resort to known low pressure handloads. It's a cost of enjoying the old stuff. No different than understanding that use of a modern multi-viscosity high detergent synthetic oil might not be good to use in a vintage car engine. If you use a vintage collector car as a 15k mile per year daily driver, it will soon wear out and have problems. Old guns are no different. So I also own some modern doubles, pumps, and semi-autos that can digest about anything I want to feed them without any worries.
Lots of guys assume that they can judge a load to be low pressure going by the velocity, the level of recoil, the sound of the report, or whether it is low or high brass. Unfortunately, it isn't that easy. So a lot of shooters are simply operating on blissful ignorance, and using loads that might not be the best choice for their vintage doubles. Most get away with it because they just don't shoot enough to notice any damage. It may take years before they finally notice their gun is a bit loose, or the top lever has moved left of center, or the stock has developed a split. Then they come here wondering what went wrong, and asking who can repair the damage.
