Depends on what you're after elk, moose, mountain goat, sheep, wildabeast. Not really a one size fits all answer.
For the most consistent flattest trajectory .338 Lapua. 30-06, 7.62x54mm and 7.92x57 are all pretty solid as well. I'd take the 7.92x57 over the other older designs. .303 is a tad light for larger game though it'd take deer caribu goats and sheep just fine.
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