How long can black powder be safely stored?

Answer 1

So long as it is in a cool dry place you can store for years. Unopened cans are less susceptible to moisture and store better, but I have powder that is more than 5 years old that I still use. It is kept in a humidity controlled 72 degree room and within a powder magazine. I also have powder that is 10+ years that is sealed, but still quite viable judging by the pound used last year.