I have loads that I use a foam card or fiber card, but that is only to keep the powder in position to avoid position sensitivity. I have never had leading from any of my cast bullets nor of any I purchased. I get them sized .001 over bore diameter and use good lube.
My DW 357 MAX would sometimes get a small amount of build up on the face of the barrel. This is between the cylinder and forcing cone and would flake off with a pocket knife or small screw driver tip. This build up woud actually be worse shooting jacketed bullets. Not much of a problem but I only have a .002" gap there so the cylinder would get hard to turn. A good friend showed me it was a tiniest bit of shaving as the bullet left the cylinder. Now I know to watch for it and clean it off with a rag after every 30-40 shots.
I have seen guys who had to buy the rod with patches made out of screen material to keep the leading out of their barrels. A change of lube, bullet sizing, or powder usually resolved the issue.
Cream of Wheat does make for good fire forming. I have used it many thousands of times for my wildcat brass. Tiny amount of powder, tissue wad, COW, tissue wad. Even these loads I work up due to pressures from COW trying to exit a bottle neck case. I was making some 30 Bower brass from 356 Winchester brass. Took me 4 different load combos before I got one to put a good shoulder on my brass. I have several friends who over guestimated and blew up a few good brass. Yes, even Cream of Wheat loads can generate too much pressure and cause gun damage or injury. Work up carefully.
I have used Cream of Wheat for buffer in a shot shell. I use a vibrator to get it to disperse thru the shot. I have never used COW between powder and a solid bullet in a brass case. Only use here is to prevent detonation. If you happen to get detonation with COW in the case, how fast will the pressures build up then.....or should I say, how fast will the pressures blow OUT then?
Good luck,
Steve