There is no reason one can not load brass shotshells with smokeless powder. You are correct, that due to them being thinner, it is best to use oversize wads. Get a 3/4" wadcutter and cut your own wads if necessary. A good over-powder wad for brass shotshells is the Ballistic Products Inc X12X wad. It seals the thinner brass shell. Use mag pistol primers. The bulky powders like Unique, Herco, etc are best. Build up the filler wads under your shot, until your over-shot on top of the shot is level with the top of the brass hull. A simple taper crimp is all that is needed. We have made this type of crimp die from pipe rearmed with a taper reamer. Don't try to roll the crimp in too much. Just enough to hold the over-shot wad tight. The Alcan/Fiocchi brass hulls I have mike .760" t0 .770" inside.
Best Regards, James
Best Regards, James