@Smokey Plainsman ,
I used to hunt squirrels with my dad, using muzzleloading smoothbores loaded with shot. We used equal volumes of powder and shot. Probably about 2-1/4 drams of powder (roughly 62 grains) and an equal amount of shot would be a good starting load for your 24 gauge. I would test a few shots on paper to check the pattern, and maybe shoot a few tin cans to assess penetration, if you have a place where you can do that.
Dad and I used hornet's nest for wadding, and it worked. We also used Kleenex when we didn't have hornet's nest, and I have used Spanish moss. We didn't have wad cutters for the good guns. I got a cheap, Spanish 28 gauge single barrel muzzleloader when I was about 15, and oddly enough, we did have a wad cutter in that size. I preferred leather wads. I got a lot of squirrels with it.
The Bevel Brothers wrote an article in Muzzle Blasts last year, I believe, testing velocity and penetration of shot loads with punched wads and with natural (loose) wadding such as tow, leaves, etc. I don't remember if they tested wasp or hornet nest. The results were sobering. Loads with the loose, fiber wadding showed something like 40% less velocity, with a comparable loss in penetration when compared to card and fiber wads. Lots of birds and small game have fallen before smoothbores that were loaded with improvised wads, but I think the key to success is to know and stay within your gun's effective range.
I really enjoy the historical aspects of blackpowder shooting, and I would encourage you to research and experiment with traditional and historic loading methods. I do. However, if you are going after game, even squirrels, you will want to use the most effective loads you can develop, or at least determine and stay within your effective range. Blown patterns and reduced velocities result in wounded animals and cripples.
Good luck!
Notchy Bob