The Ideal and Lyman lubrisizer unfortunately size the entire bullet to one diameter. The purpose of the R.E.A.L. Bullet was to have different diameter rings around the bullet which are to be engraved into the rifling upon being seated in the muzzle. Rifling Engraved At Loading. (or something like that) hence the name. The last, top band around the bullet is intentionally larger than the other bands. To size them in a Lubrisizer would defeat the purpose and make all the bands uniform.
Lastly, sizing in a lubrisizer is good only if the bullet is sized properly for the intended bore and rifling. Yes you can get a 50 cal die, (for 50-70 and 50-90,) but it is likely to be too large for a 50 cal muzzleloader. Dipping the bullets in melted lube and allowing to dry or smearing the lube on with the fingers is about the best. Unless you are takng part in a battle, how many bullets do you need in one day or week anyway.
I shoot 450 grain minnies in a Zouave, for hunting. Ten bullets for sighting and three or four for the hunt and thats it. (Most of the time I shoot patched ball)