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.

I use the 25ACP conversion which does an 80% job of eliminating the problem, and just make sure I run a decent spit patch down the barrel in 3-4 short strokes so it doesn't have a chance to get stuck. End of all problems with 777, and my breech plug is clean in 15 sec.