Am I right or wrong in thinking I don't need to spend $17 or more on 10 or 15 "muzzleloader bullets" in (or with) sabots in the pack?

I have a .50 caliber Knight Bighorn.

Can't I just buy .451 or .452 caliber projectiles from Hornady, Speer, etc. and "sleeve" (is there a a more widely used term I should know) them myself in some .50 cal sabots bought in bags of 50 or whatever for $7?

Any help, information, or direction greatly appreciated.

thanks!
john