I wrote Barnes, and the very nice gentlemen advised around a max load of 38 grains of 4198, but I expect I'll start off around 35, and head up a grain at time. I loaded 35.1 for my first batch behind a 220 grain horn flat point, it shot fairly straight, but the recoil was rather stout, surprisingly so.
They said that they have not tested the 210gr in 375win, and were not to be held accountable for the recommendation. He advised care, but also seemed excited by the prospect.
I'll look into a factory crimp die, the idea has a great deal of promise, for these odd loads espiecally. I'm guessing they are caliber specific, are they not?
Take care fellows, good shooting.
Steve