If we can deal with the minutiae of technical terms first, ‘calibre’ is really the diameter of the bore of a gun before the rifling is cut or impressed; which means that .30 is the calibre, .308 is the bullet diameter and .308 Winchester is the name of a cartridge.
But English is a living, changing language and it doesn’t do to be too pedantic about precise meanings as long as we understand each other.
So I presume what you are really asking for is my thoughts on the most suitable cartridge?
And can I also presume, since you have asked the question, that you have not been seduced by reading an article extolling the virtues of a .280 Remington Ackley Improved, a .243 Catbird, a .333 OKH or some other curious and interesting – but quite unnecessary – cartridge?
For more than 20 years I have given the same answer to this question and that is, “If you need to ask me, get a .308.”
By which I mean, of course, the .308 Winchester, not the .308 Norma Magnum or some other monster.
Try various brands of ammo and different weights of bullet to see what the rifle prefers but remember that light, fast bullets can do an awful lot of meat damage so it’s best to stick to at least 150 grains – and preferably 165 or 180 grain bullets for the larger species – provided your rifle shoots them accurately.