I shot some 1880's head stamped .45-70 ammo in the early 1970's. It was black-powder ammo and all shot fine. We were shooting at a steel 55 gallon oil drum at about 80 yards. I was shooting it out of a trap door Springfield. We had been shooting the oil drum with a whole bunch of more modern rifle rounds. (.30-06,.30-30.8MM Mauser) The modern stuff just poked holes in both sides. You could hear the .45-70 rounds hit. The drum was already pretty shot up, but the .45-70 rounds rocked the drum and started to bend it.
I also got a deal on some Turkish 8MM Mauser ammo in the late 1990's. It was dated in the 1930's. It shot fine. I think I only had a few that would not fire at all. Also had a few that needed 2 hits on the primer. Out of about 5,000 rounds I doubt if I had trouble with 100 of them.