I would rather use a .375 than a reduced .500 NE load. Ms. Brooks of Barnes Bullets used a reduced .500 NE load for an elephant and it took her 19 shots or so. The problem was poor penetration. (But you will not see that story in their advertising materials...)

However, here is a reduced .500 NE load which I use that regulates.

45.0 grains XMP5744 behind a 500 grain lead bullet. But it would work with a 570 grain bullet too, although you might want to increase it by 5 grains or so. Expect something in the neighborhood of 1500 fps.