I'm actually using a Brown Bess musket rather than a true "shotgun" to hunt snowshoe hare. It's a .75 caliber or 11 gauge, but puts out a really decent IC pattern at 30 yards with 1 1/4 oz of shot over 80 grains of 3f, with a lubed fiber base wad and nicked over-shot card.
Thought anyone taking a muzzleloading shotgun into the field would be interested in what I've come up with for handling the shots and wads/cards.
The shot flask is made from 3 oz leather, and the nozzle is an old style available from Track of the Wolf, and probably other sources. Delivers a pre-measured 1 1/4 oz or 1 1/2 oz charge slick as a whistle. When I build another I'm going to make it smaller and put a single grommet in the bottom. Smaller, because even fist-sized holds 3 pounds of shot! And the single grommet at the bottom will allow me to hang it upside down from a bag strap if I want, for even more convenience.
The little "wallet" is no bigger than a deck of cards, yet holds a couple of dozen of the lubed fiber base wads and as many over-shot cards as you can fit into the little side pocket.
Altogether, a handy setup. I could get by carrying nothing more than that and a powder horn. But it's in my nature to carry more, so I built a fowler-style shooting bag with a 2" gusset to hold those things plus the extras I always carry. No picture, but it's made with oiled leather rather than veg tanned.