Why would it be corrosive? Even the Commie ammo that we see that is listed as corrosive is that way because the primers contained Mercury. I don't know of any US made ammo that used Mercury in the primers.
The loose stuff mentioned is just as likely reclaimed machine gun ammo that's been de-linked and the tracers removed. The CMP has sold tons of that stuff.
I know for a fact that the 47 head stamped 30-06 rusts like crazy, as does the 40 headstampted 45 ACP steel cased stuff out of spam cans. I can also vouch for some of the 7.62x39 being corrosive as well. there is more to rust than mercury, salts in the primers draw water out of the air but also bring it to the metal causing rust and a lot of ammo prior to the 70s had salt in the primers as preservative.