I worked a suicide case where an elderly fellow shot himself on Christmas eve several years ago. He used a 22 shell out of an ancient box of I believe Remington UMC Old Green and Red Box. If I found the box it would have been on the mantle with some of my other ancient ammo boxs. The 22 shell worked as good as new.
Properly stored they last a long time.
Tip for Today: you can store 14 each Federal 550 packs in a GI Fat 50 ammo can. Might be handy to know some day.