RE: I'm ready...
The bullet itself is a full caliber flat point conical. The sub base it considered a "wad" - it's purpose is to insulate the base of the soft lead bullet from the heat/pressure of the magnum powder charges. This combination is CDOW approved - as is the Powerbelt. Neither are considered a sabot for regulation purposes. These loads, with the sub base, have shot very well in my Black Diamonds as well asmy Omega.
Incidently, this is the only bullet I have used in conjunction with the MMP sub base that has shot considerably better with than without. I tried several other lead conicals that shot the same or worse with the sub base. My theory is that the front of this sub base very closely matches the hollow base of the 410 Great Plains bullet. Other posters have reported using the sub base with hot sabot loads and noting an improvement, however. I think they were originally developed for use with smokeless loads in the Savage MLII.