Cream of Wheat is a common filler. Also, are you using a grease cookie or grease wad?
Some folks use carded wool. How much do you want to load down? You want to compress the powder slightly and make sure there are no voids, no matter what I knew a fellow that shot 40 grains, a card board wad , some cream of wheat another card and a 1/4 inch thick grease cookie. He won alot a matches with that load and an old Ballard.