Use loads listed in manuals for the 28 gauge, and you won't go far wrong. Consider the age of the gun, and stay with the lighter loads. You might find some loading info in the Dixie Gun Works Catalog. Also, check Bob Spenser's Website, Black Powder Notebook, and the article written by V.M. Starr located there to see if there is a recommendation for this small guage.( No, I just checked, but he does list loads for the small 28 gauge.)
For wads, you should be able to find wads listed for the .58 caliber rifles, and they should work in your smoothbore. ( 24 gauge = .579"). Circle fly makes them, and I have seen them for sale at Track of the Wolf's catalogue. They may also be for sale at other suppliers, and never overlook contacting Circle fly directly to buy them. You can get buy using only the OS cards: Use 4 of them over the powder, and two of them over the shot. punch a hole in each of the cards, off-center, and then put them in the barrel so that the holes are NOT aligned with holes in the next card. Try 3,6,9 and 12 o'clock positions for the ones over the powder, and 6 ans 12 o'Clock for the two cards over the shot. The hole lets air escape so the wads don't fight you by dieseling in the barrel as you seat them, and you don't turn edges, so you break the seal. The reason for using wads is to seal the gases behind the wad to aid in complete burning of the powder. The two OS cards you put down over the Shot will make sure the load does not shift forward in the barrel while you are carrying the gun in the field.
By comparison, 20 gauge loads( larger gauge) run from 2 drams( 55 grains FFg) to 2 1/2 Drams( 69 grains FFg). The 28 gauge loads run only 1 3/4 Drams( 48 grains FFg) to 2 drams. Shot charge for the 28 ga. run from 5/8 oz to 3/4 oz. 20 ga. shot charges run from 3/4 oz. to 7/8 oz.
Looking at those ranges of recommendations, I would suggest you try 55 grains of FFg, and a shot charge of 3/4 oz. in your 24 gauge. That is about an equal amount of powder to shot, by volume, using your adjustable volume powder measure, set at 55 grains.
Its nice to see you are restoring an old gun. Just make sure you have the barrels check to make sure they are sound.
