Bullets for the 45-70 will be either .457 or .458. You can use them in a .50 caliber ML with MMP orange sabots which are made for that diameter bullets.

The .451 and .452 bullets made by Nosler, Speer, Hornady, etc., are not special run ML bullets. They are made for .45 caliber pistols like the 45 Colt, 45 ACP (the lighter bullets), and the .454 Casull. They work so well in MLs because they are built for impact velocities suitable for a hot pistol load that is similar to ML velocities. Harvester, MMP, and others make .50 caliber sabots for use with .451/.452 bullets.