Some years ago, I was trying to find "lowest pressure" rimfire .22 Long Rifle - I know what SAAMI sets for pressure levels for that cartridge today, but the rifle was probably made 1896 - several decades before SAAMI existed as a formal organization - I do not know what was used as a pressure standard then - or even IF a standard existed for North American makers of rifles and ammo. But many makers were stamping their stuff as ".22 Long Rifle" - I have, so far, no reason to know that "22 Long Rifle" in 1896 implies the same thing as "22 Long Rifle" in 2026. But I never did find out what standard existed then (pre-SAAMI) that made that so. And, about no maker publishes the "pressure level" of their ammo. Even worse (for me), I received a similar aged single shot .22 made in Germany - so what was the standard then, in Europe - was it the same as North America?? Up until now, I have only used CCI Quiet in those guns - thinking that the lower muzzle velocity might mean lower breech pressure - but some shotgun reloading information tells me that might not be so.
Hence, I am not sure that what is stamped for calibre or cartridge on the barrel means much, except for the chambering, originally - I am sure the original "proof test" proved that barrel, action and bolt lock-up - but wear, deterioration, rust, etc. might have changed that. I am not sure that some steel changes much with age - I read there are 500 year old Samuri swords that are still limber and flexible like they were originally. But that may or may not apply to "ALL" steel, especially the stuff used in barrels by various makers, over the centuries.