most of what i shoot are reloads that i make. most of it never sits on the shelf for more than a year. if i make something up (like special accuracy loads for hunting), i will seal both the bullet and the primer so no air can get inside of the brass. all of my long term ammo, sets in military surplus ammo cans with good seals on them. 30-06 shells that were made in the 40's are still being shot today that were stored in ammo cans. at my age, if it lasts another 20 years, it will probably last longer than i will.