With proper storage ammo shelf life is very long. I heard folks shooting soft iron cased .45ACP loads from WWII (made at same time as copper-less penny I suspect). Years ago I have shot bunch of 20ga paper cased slugs sold by either Sears Roebuck or J.C. Penny. There was no failures and ammo was about 30 years old when I shot it. The problem is just one squib can create an obstruction and if not noticed next discharge will result in bulge or worse.