I decided to do an abusive ammo storage test a couple years ago and couldn't kill any. I put many rounds in a big ziplock with a wet paper towel and put it outside on a steel table where it would get hot and cold along with some direct sunlight for almost two years with a couple trips through the freezer. I occasionally re-wet the towel since ziplocks are permeable and several times the inside of the bag was sweating. There was .22, .38, .30 carbine, 9mm, .223, 7.62X54R, 12ga., black powder, pyrodex, and probably some others I forgot about. There was a mix of modern factory loads, reloads, and milsurp. There were some that seemed a bit weak but not enough to say for sure. I know this doesn't define what should be done for proper longterm storage, just a test to confirm that ammo isn't all that sensitive to storage conditions.