If the ammo is kept in a clean, dry environment, it has a very long shelf life. I have never heard of the manufacturers stating one, but I have store bought shotgun shells well over 25 years old (shot size seldom used, etc) that performs as best I can tell as new. Ducks I shot last week end didnt know the difference with shells I bought in 82. (I dont get out much for ducks- obviously) .I have used up mid 1950s production powder and primer reloading components that functioned as new. Of course, if left in a high humidity environment, dirt, exhaust fumes, etc. factors could change.