Maybe the solution is to install a cup into the shot load at the top of the shell with the open end in the shell to contain more shot. Don't ask me how to keep the shot from spilling out as you install the cup. Possibly slotting the cup, installing shot through the slot, then pushing the cup into the shell with the slot inside the shell? This method would eliminate the use of a different case. Jon's suggestion to try Unique, Herco, or AA452 is a bit confusing since all are way faster burning than the 410 powders and would raise pressures into the stratosphere with a 3/4 ounce load or heavier.