This brings to mind something I read in a book called "Hatcher's Notebook." Major General Julian Hatcher was in the ordinance dept for much of his career and wrote many articles in The American Rifleman.

Shortly after the '03 Springfield was adopted by the US Army it was found that some receivers were improperly heat treated at the Rock Island Arsenal leading to some failures and injuries.

It was finally found that because the smiths weren't using pyrometers but were judging the forging by eye the temperatures varied widely depending on whether it was sunny or overcast. So as good as some of those old blades are there is probably more variance with those than with the current production.