RE: Stocking up on ammo
Follow proper storage procedure and the ammo should store a lifetime.
-Keep away from moisture, store ammo in a sealed container
-Do not store ammo directly on the floor/ground
-Keep ammo from excessive heat and cold (not below 25 deg and not above 100 deg)
-Aviod metal to metal contact
-Make sure ammo is clean and dry before storing
-It is usually best to leave the ammo in it's origional packaging if possible
For long term I wouldn't put the ammo in the basement or the attic (moisture and heat) or out in the barn. I also would not spend $$$$ trying to make nitrogen purged storage boxes or vacuum sealing the ammo, it is wasted effort and just not required to store the ammo for say a target of 30 or 40 years. I would also check the ammo out every decade or so, take a look at how it has been holding up. Happy stockpiling.