My dad gave me a WWII Mauser and some old ammo, took it to the range and fired off a number of rounds until, the slide wouldn't close completely. A round had gone off with reduced pressure, bullet was in the barrel, luckily close enough to the breech that the next round wouldn't chamber. Lucky me. Used a wooden dowel to drive out the bullet. Gun works fine to this day. I don't know how old or the history of the ammo. On the other hand, I too have shot ammo that is pre WWII, no problems. As they say, "Be careful out there"