lilabner,
I usea lot of old powder.
I'm currently using a can of DuPont 4350 powder.The can is a 'collectable'.
I get better groups with it then I do with my new IMR 4350 powder.
When powder goes bad it looks bad and smells really bad.
Old powder shows its age by emiting a little smoke when you pour it out. My old 4350 oowder does this. Don't worry.
When the powder smoke turns redish or sorta purple,it's going bad. When the grains stick togther,it's going bad.(like they would do if they were damp).
When you get a strong 'solvent' smell,it's going bad.
When it developes a strong acrid smell,put it on the garden.
Frank