Knurl them up. They might shoot great sabotless but i dont know the twist. A 250gr might still be ok in a 1-30 or 1-28 if you can shoot them fast enough. Lee sells a standard .454 sizing die if you wish to keep them uniform in size. A knurled .454 OD should load in a .453 as long as it was not tight going through the .454 die.

Ive also used a .406 in a Harvester Crushrib with ok success. Some guys use 41mag bullets with a Harvester CR in a loose 45cal bore. Hawks can make you some custom sized 40s if you really need them. Just avoid his "pointy" bullets.

BTW the old Knight brown sabots are even larger than the MMP Tan. I think the new ones are the same size though.