In the smaller bores, such as the 24 gauge trade gun or maybe a 28 gauge smooth rifle, start with the same charges you would start with when working up loads for a rifle of that caliber. There has been a lot of comments about what lead to cast those pumpkin balls out of. After 10 years of experiments and over 100 pounds of powder down the barrels, I honestly don't know. Personally, in my Brown Bess, I use wheel weight lead for targets and plinking, and pure lead for hunting. I don't know, never having recovered a ball shot into an animal-including a buffallo.
Some techniques seem to work better with smaller bores than larger bores, and vice-versa.
Don't be afraid to experiment, but you might try the tips for bore sizes close to your own first. More specifically, REAR sights. Some guns were originally fitted with rear sights by their makers. Examples would be some of the early trade guns, or the smooth rifles. Many others were retro-fitted with rear sights by the users.