I have no scientific data to cite, but I think modern ammo which is kept in a temperature range of between 65 and 80 degrees Fahrenheit, not exposed to moisture or penetrating lubricants; should be good for at least two decades.
NRA Life Member - Orange Gunsite Member - NRA Certified Pistol Instructor
"When plunder becomes a way of life for a group of men living together in society,
they create for themselves in the course of time a legal system that authorizes it and a moral code that justifies it." Frederic Bastiat