I’d think a ~ 400 grain blunt/flat nose cast bullet traveling in the neighborhood of 1,800 fps should kill whatever I’d likely be shooting.
The market is flooded with 7mm RM rifles and they can be had pretty cheap (I like the 7mm RM a lot by the way.)
Re-barreling to 458 would likely increase the value of the rifle about as much as the cost - maybe.
Welcome, Bugger, get that .458 WinMag shooting and become a Knight of the Square Table.
400-gr FN at 1800 fps from the .458 WinMag would make it into an elk killer like Elmer Keith preferred in the timber with .45-70 Lever Action.
Just size it properly, gas check might be preferrable to plain base, but not necessarily, BHN 15 or higher.
Success is guaranteed by trying AA-5744 with no filler.
Start about 40.0 grains and quit at 1800 fps.
Too many other powders to shake a stick at will do it also.
