I've got some old PB powder that I used to use for my 20ga target loads. I haven't used much for quite awhile and still have several pounds of it left. I think that it could be 20 yrs old. I know that powder starts to smell funny if it gets bad but this stuff still smells like the new powder that I have. I have been using it in some 12ga loads to get rid of it and it seems to be working OK but when does it actually wear out?