I had some Remington caps that I purchased in the mid 1960s that I had kept (in the tins of course) stored in a dry place and they worked fine. I also had some ALCAN musket caps from the same time period and they worked fine as well. Years ago, I had a partial tin of caps that belonged to my grandfather that he used with his rifle. He was born in 1867 so I'm sure that these dated to the late 1800s. For kicks, I tried a couple of them and they worked fine. Like anything else of that nature, if stored in a dry environment, they should last for many, many years.