FWIW....

The can of Pyrodex RS I am using right now is at least 7-8yrs old. (My dad gave me this can about 4 years ago when he quit using Pyrodex. I didn't start shooting it until I ran out of the powder I was using about 2yrs ago). It has always been properly stored. I shot last week with it...it shot as good and strong as any new can I've ever shot.