I have been using steel shot reloads for the past few years and I have had a few loads recently that shot funny and left a lot of unburnt powder in my barrell. Did my powder get wet, or old? My recipe is and has worked for the past 6 cases without a hitch.

Thanks for any insight on this issue.
2 3/4 Cheddite hulls(and Kent Hulls)
36 Grains Alliant steel powder
1 OZ #2 steel shot
Federal 209A primer