MMP makes .50 caliber sabots that fit .458 bullets.
Perhaps they're thinner and have a smaller diameter than the TC Sabots.
I would ask MMP what the diameter is of their orange .458 sabots.
MMP also makes a Ballistic Bridge Sub-Base that may provide a benefit when firing such heavy saboted .458 bullets.
They can provide:
*Additional Gas Seal
*Cushion/protection of Sabot Base
*Improved Accuracy!
http://www.mmpsabots.com/
What rifle model do you have?