I am casting the 500 grain Lee .458, sizing it to .451 (three step process, .458 to .455, .455 to .452 and finally to .451) and shooting it in a .50 Encore using Harvester sabot. My accuracy isn't real good yet, only 3" group at 50 yards. Still playing around with slight bevel on the base of the bullet, varying the powder charge, etc.
alan
updated- and clarified.