Seems like a strange process. Forcing a .50 caliber bullet into the .451 die I would think you have to have a good deal of 'finning' around the edges of the bullet. Plus, if the die is open ended, as it appears to be, how do you trim the nose & base? The parent .50 caliber bullet would have to weigh more (by at least 5%) than the finished .451 bullet to ensure full displacement in the mold. Seems like an awfully complicated method to make bullets! I think you'd be better off just shooting the cylindrical .451 bullets, they've been proven to upset enough to fill the hexagonal bore.