Thanks Sharpsman, I'm about halfway there, IIRC you pointed out a water trough at what I thought was 1000 yards across that Red River bottom land and said I could hit that when I learned how to run that rifle the day I bought it from you.
HMMMM:
.458 diameter and 570 grains at 1381 fps vs .512 diameter and 720 grains at a guessed 1365 fps, bet they'd be running close to neck and neck, with the momentum part of the equation going to the Big 50.