I got some .50 caliber Harvester Crush Rib sabots recently - in both the .451 and .429 versions. Haven't used the .451 (black) ones yet, but tried the .429 (green) ones with some Nosler HGpistol bullets. Even though it said "High Pressure" on the package, they were coming apart with 130 grains of Pyrodex pellets.

Intend to try the .451 versions sometime in the near future. They don't, IMO, load all that much easier than regular sabots. If you are looking for Powerbelt loading ease, you will probably be disappointed.