Jorge - this oddity of the behaviour of the 400gr. TSX might be merely an indication it is a bit too long for the standard rifling twist, therefore the preference for the lighter, shorter bullet. The 350 should penetrate just about as well, and exit about anything shot with it. Coupled with that, it's slightly higher velcity would make for better use on long range plains game.
; When a bullet is properly stabilized, it should not reverse if maintaining a long shank. The solid metal bullets are long for their weight, therefore requiring a slightly faster twist to be properly stabilized. I am sure there are some .416's out there with faster twists, just as there are .458's with 14" and 15" twists, much faster than needed for normal stabilization, even with normal 500gr. lead/guilding metal bullets.