My personal experience is with pyrodex there is a crud "cylinder" over an inch or two at the bottom of the barrel, does not really affect loading for a few shots but you can feel it if you run a wet patch down. With 777 in my Omegas, I got a true crud ring right where the seated sabot sits on the powder. If I did not get enough spit on a patch and just rammed it down there after the shot, it often jammed the jag in the barrel and I had to pull the plug to get it out.