Gottcha. I'd probably open up the chamber neck to allow seating the ball in the case mouth.
: Your idea of dropping he ball into the chamber then seating a ctg. behind it will be OK as long as the wad at the top of the case contacts or very nearly contacts the ball and holds it there. YOu may find you don't have to shorten the cases at all, as the ball is only groove diameter at the case mouth - not much difference and with then normal tiny bit of relief (throat) in the chamber (probably) the ball will sit perfectly at the case mouth.