I am having trouble determining what bullets you are using. Powerbelts are not sabots. Are you really referring to sabots or powerbelts?

Most powders (including pyrodex) will leave some form of "crud ring". 777 is the worst by far, but each shot with pyrodex will make it harder to load subsequent shots (and IMO affect POI somewhat). In most guns, that is not enough to worry about one follow up shot (including 777). When I did use pryodex, about 3 shots was max before bullets got too hard to load.

BH 209, on the other hand is one of the few powders that doesn't require swabbing for an entire shooting session. I have shot over 30 shots without swabbing and no diffence in POI. So, bottom line is that even with pyrodex, you will have to swab often. how often you will just have to try and see.

As far as what results I have had with powerbelts: Accurate, but I believe there are better built bullets out there that I have more confendence in, so I don't use them any more. If I were forced to use them, I would never exceed 100 gr of powder. Pushed too hard, they will come apart. In other words, 100 gr of powder will many times mean better penetration than 150 gr.