A post on the topic!

Reading the comments rather than the title.

Best all round rifle in the world.

Key points -> all round - various forms of hunting.
and -> in the world - handle hunting the world around.
and -> best - to me best does not mean expensive, it means best for the job.

The calibre has to handle the entire world species so only one, the .375. IMO the ammo needs to be widely available so it is the .375 H&H Magnum. I don't have much time for the latter pretenders anyway. Why not a 9.3mm? Because while good, they are not legal for DG in many African countries.

The make or rifle. I'm not going to name the make other than saying a Mauser 98 actioned rifle. Various makers, of the past and present. Available second hand, custom, etc.

One can hunt elephant with a .375. One can hunt a deer, or a pig. It has a similar trajectory to a .30-06 so with the right bullets one could even use it in the mountains for medium range shots. As one can do on African plains as well. About the only limitation is small game such as rabbits, hares, etc

Myself I think there is NO all round calibre. One needs at least a small game rifle as well, though a shotgun will do that.

My .375 H&H Magnum is a M98 Whitworth rifle bought second hand.