A couple of points: Ken Mollohan of the Cast Bullet Association enthusiastically promoted the use of Cream of Wheat (COW) as a filler when using reduced loads of smokeless powder and cast bullets (primarily wheel weights + 1% - 2% tin) as a means of reducing bore leading. It works as Ken claimed, but accuracy often suffered in the process. While I've used fillers, both cereal and polymer (spherical shot buffer) in my .30cal. (metric & English) centerfire rifles with cast bullets, it has always been in very small amounts (0.3cc, 0.7cc, or 1.0cc, via Lee dippers) with one very slow military surplus extruded powder, IMR 5010. Understand, I did so to increase the pressure and hence the cleanliness of the burn, as evidenced by significantly lower extreme velocity spreads and standard deviations, NOT to reduce bore leading (which wasn't a problem in the first place). Would it scour the bore in muzzle loaders using BP as well? I have no idea, but with a proper lube, patch thickness and round ball combination, I wonder whether there's so much fouling as to be problematic. I use Graf's (Wano) or Goex powder, both FFg and FFFg, with Winchester Sutler's Moose Milk, Ox-Yoke's Wonder Lube, or 103 Lube, wipe between shots and don't have much of a fouling problem. If you're adventurous or don't mind another loading step, maybe "English powder," say 10 -20 grains (volume) is worth trying. Btw, I no longer use cereal fillers in my centerfire rifle loads as I disliked the additional loading steps.