While they can go bad especally if gotten damp they normally store well for a couple years,Cayuqad may have pinned down the problem if you put them in upside down or if they have gotten damp; you might also check that your touch hole from the primer to the powder is completely clear.
I also remember that some of the conversions used a #11 cap if thats the case your best answer will be to switch to black or Pyrodex P to get better ignition.
Sabots should work just fine once you get the right petal thickness. Lee