RE: How long will powder stay good?
The main thing is how well they are stored. I always store them in the original container, in a cool dry place. I also make sure they have no contamination. I have a box of Pyrodex Pellets that are now pushing over one year old, and I was shooting some of them the other day with just fine results.
The main thing with any powder, dry, cool place, original container, and something to absorb moisture would not hurt but not necessary. I have them in an original cardboard case that they shipped Goex to me. All my powders are stored in them boxes.