I like my Ruger 1 in 45-70 and it is a cupcake to shoot with factory loads. It will get you out to 100 easy. Ballistically, 8 million dead buffalo can't be wrong. And they are huge beasts, known to get up to 3k. They are also truly thick skinned game.

I use a Burris signature safari scope, for when I crank in a heavier load. Good eye relief! The #1 will handle really stout loads, and kick accordingly. I shoot really heavy loads from the stand. I zero from a heavy camera tripod. Bench shooting an elephant rifle gets brutal fast. Both Buffalo Bore and Garrett have heavy rounds for sale.

The 338 is really a different round. It is designed to reach out and hit hard at longer ranges. It starts in the 200 grain weight class and has significantly more frontal area than the 300 magnums. Much to like there.