For your .50 caliber ML, a readily available choice for sabots/bullets would likely be .450"-.452". Think of .45 caliber pistol bullet diameter. These can be purchased in a variety of bullet types and weights. Plus, offer good accuracy and performance. While you're at it, also consider .44 caliber saboted bullets. These are good performers, too. Hornady .44 caliber, 240 grain HP XTP bullets a longtime favourite choice for many hunters.
MMP does manufacture sabots for .458" bullets though, if that is your preference. Likewise: Harvester. These can be purchased from Sporteque.
As for accuracy and performance, your rifle will soon let you know which load combination it prefers. I'd suggest starting at 80 grains Ffg,(or equivalent), for hunting loads, then work up in 5 grain increments. In most cases, around 90-100 grains seems to be the sweet spot, for .50 caliber rifles. With some rifles delivering good accuracy and performance up to around 120 grains. Only load experimentation will tell you which is best, in your individual rifle.
Yes...you can load them up to the max (150 grains in some rifles) if you like. But, it's been my experience that the recoil and often poor accuracy that comes with a bad flinch, often negates any power advantage.
Your overall accuracy should remain about the same, depending on bullets chosen for plinking, versus hunting. If the same weight and powder charge.
