I read a section of a Winchester book that recommended piling it loosely in a mound, trickle a line to it like an in old western, and light it. It will burn off easily. Remember, it's a "propellant" - not an explosive. It only causes a serious bang when under pressure - out in the open it just burns (I've tested this myself, not just a rumor!).
But seriously, if it's been stored properly, it should still be fine to use, unless you see it looking funky or smelling of ammonia. They are stable compounds with very long shelf-lives. If you seriously don't want it and are near by, heck, I'll try reloading it just for an experiment!