I was reloading for mine over the weekend. GI brass (though I use commercial brass as well), CCI large rifle primers, IMR4895 and Hornady 150 grain FMJBT bullets.
I sorted out (after resizing, trimming and priming) the following cases. I have to wonder where they've been since the original rounds were made/loaded and how many times they've been reloaded.
WRA 57 (3) - Winchester Repeating Arms Co. in CT
SL 54 (2) - St. Louis Ordnance Plant in MO
SL 43 - St. Louis Ordnance Plant in MO
LC 42 - Lake City Ordnance Plant in MO
LC 43 (2) - Lake City Ordnance Plant in MO
FA 54 - Frankford Arsenal in PA
FA 43 - Frankford Arsenal in PA
Looks like the oldest is about 75 years old.
I reloaded quite a bit of LC 68 and 69 brass. Old, but not as old as the ones listed above.
The rifles and the ammo/components are still going strong long after the people and plants that made them are gone.