"Modern" lead shot is fine. Some of the lead alternatives might require something between them and the barrel steel.
Except for when loading the Skychief Load, I never use nitro-cards or thick fiber "cushion" wads between powder and shot. I know one very successful muzzloading hunter, who takes many pheasant, squirrels, rabbits, foxes, crows, wood pigeon, and more,,,, with various size bore smoothies,,,, and he only uses thin cards. A stack between powder and shot and another one or two over the shot. Every few reloads he puts a dollop of lube between cards in the below shot stack.
I've seen guys successfuly use leather wads as well.
I use powder, thin card (sometimes replaced with grocery bag paper 1"×2" folded to 1"×1"), then some type of soft lubed wad such as felt or tow/faux-tow, shot (either loose in a Skychief Load or in one of my paper pre-made shot cup/cartridges), then a thin card to hold it in.
It all is more complicated to write and to read than it is to do.
No tow? Cut 4" sections of hemp or sisal rope (4" is good for a 20 gauge) and section it into the basic strings that make up the rose's thickness, two of these work well for me, shred those into loose fibers (lengthwise) roll into a ball (like making meatballs) adding lube as you do so. End result should be a ball of fiber that is about bore diameter. I pull it slightly apart, like making a little nest, at time of use.
