Thought I would give an update after receiving all my sabot samples in the mail last week. Testing was done by removing the breechplug and pushing load through from muzzle all the way out the breech to test resistance.Results as follows:

Knight black sabot with .451 Barnes MZ Expander- Nice tight fit. Concern: Sabot only en-cases 50% of bullet. Not sure if this is an issue or not.

MMP HPH-24 with .458 bullet- Very tight fit

MMP 3pedal EZ with .458 bullet- Nice tight fit but one of the pedals broke off when pushing down the barrel.

Harvester Black Crushed Rib with .458 bullet. Nice tight fit.

Harvester Red crushed rib with .458 bullet- Very tight fit, about the same as HPH-24.

So in conclusion it looks as though all options listed above with the exclusion of the 3-pedal ez sabot will be given a try at the range this coming spring. I think the Black crushed rib would be my first choice as it offered a tight fit but not to tight so you have to fight it to get down the barrel.