Well I have had "open" powder and pellet around the house for over a year and it shot fine. I had some Clean Shot that was over four years old and it shot fine. I think a lot has to do with how you store it between use. I keep it in the original container when ever possible. I make sure the powder caps are on straight and tight. Also I store the powder in a cool dry place. So far so good. I usually buy my powder by the case and some of it will sit around the house for some extended times...