A lot of WW2 Germany made ammo came into the states in the 50's and 60's. Almost all of it steel case and some of it had begun to show corrosion on it. By today I would not be surprised if most of the steel cased ammo is gone one way or another. The turn around time on it was short as it was shipped out to the front almost as fast as they could make it so the cases were not really well protected against corrosion. The German machine guns were eating up a lot of it on the eastern front. I do not think all that much was captured by the Russians as they would pick up the rifles after a battle but the ammo in general was just left on the battlefield.