Mike,
Total guess here but is it the Yugo brass cased on strippers? 40 to a box and 28 boxes to a case correct? If so I can't recall if my hermatically sealed tins were still sealed or not. I know the Yugo 8mm cases were SELDOM actually air tight.
Heres my opinion. The Yugo ammo is FABULOUS ammo, probably dated late 70's and gorgeous. Remember this IS corrosive. Period (if Yugo of course) I shoot 1938 Turm 8mm with no hesitation on the primers at all, I shoot 1951 Yugo 8mm with no issue (a few double strikes) and countless other countries of old milsurp ammo. So, if you open a can now and keep it in a cool dry enviroment ( I recall you live in a dry area) I see absolutely no reason this ammo would suddenly go "bad" in the next say...35-40 years.
Hmmmmmm, I have shot German 8mm surplus and Turk surplus (powder may be aged in turk) and have faired just fine. Under what conditions were they stored?? Then put on a ship, slow boat to us to sit until sold to me and sat on the UPS truck on a 95 degree day. It has faired just fine.
If your worried about it. Open the case and then store the ammo in a 6" PVC pipe with caps glued on the ends. Cheap and easy, can be buried etc.
Thanks for the .380 dies, they showed today. PERFECT!