It appears that Hook is already a little familiar with casting conicals. In this case a REAL.
Sizing for muzzleloader

Is also appears he has a CVA Acurra and a older BlackDiamond. I would try the standard Harvester smooth sabots first if these are for the Accura. The Crushrib may be a better fit for the BlackDiamond. A Lee sizing die is cheap but likely not needed if casting for sabots. Like $20-22 cheap for .451, .452 and .454 They do come in handy however if a sabot is just a tiny bit too tight. Just resize the bullet a little smaller. Works great, ive done it many times.

NOE sells a (sorta) adjustable sizer. You change out a $10 sizer bushing and push rod. The body assembly though is around $40. Could be a useful item if casting for both 50cal sabotless and sabotted.
http://noebulletmolds.com/NV/index.php?cPath=564_104