Cardstock cut to the ID of the shell, (the OP suggested using a sharpened case in a drill-press chuck, cuts perfect circles) Card over powder, Birdshot, then capped with a soft lead ball, just large enough to shave the edges off and seat well when pressed into position. Lead fouling, sure.. not something you want to sit and put through your gun all day... but you have a mix of both worlds, a Slug for coyote or any approaching rabid animal, and a decent spray of shot with it. Edit/afterthought... Anyone with experience capping a load like this with a standard Boool-lit to aid feeding in a Semi? Primarily these loads DO go into Revolvers, but options are nice.