My measurements show the Harvester BCR and Smooth sabots to be extremely close in loaded OD. The MMP 50x45 HPH-24 sabot is also very similar. All 3 do feel like they require different amounts of pressure to load.

The BCRs are the easiest to load and its a toss up between the Harvester Smooth and MMP HPH-24 depending on outside temps. When its cooler, the MMP feels like it loads a tiny bit easier to me.

The RED Crushribs are by far the hardest to load and measure roughly .508. MMP's Black Short is as large but the shorter petals offer less resistance going down the bore. A BCR with a .458 bullet instead of a .452 or .451 is also around .509 and very popular in large bore 50cals.

Keep in mind, not all 45cal bullets are .452. The Harvester PTs are normally .451 and so are all new Parker BE/MH bullets as well as most Barnes. Some older Parkers are slightly smaller. I run most of mine through a cheap Lee sizing die to keep them all the same size.

BTW MMP will also send you samples if you call them. Both companies deserve high marks for CS in my opinion.