Last week,i had wondered the same thing! I called Hodgdon powder company and ask that question. A fellow named Cody talked to me and said " As long as it is kept dry,it will stay good the same as black powder."
I bought a pound of it,i can't remember how long ago,but it has been years! I've had it stored in a dry place. I am going to use it this week to shoot an inline 50 cal and some sabots,for my son.
I guess i will find out?