As a recent convert over to 777 primers from w209’s I can say there is a huge difference in the dreaded crude ring that forms, both with 777 pellets and IMR white hots.
Regular W209 - 3 shots and you can really feel the crude ring impeding the seating of the bullet/sabot, even making it impossible with certain brands of sabot.
777 primer I could go 5-6 if needed and fouling is still much less.