Not to be completely contrarian, but there’s a considerable body of knowledge that says smaller calibers will reliably kill big animals like asiatic and African buffalo very effectively with quality bullets and good shooting. Leaving aside regulatory constraints, there’s no reason why an experienced resident hunter shouldn’t use whatever he thinks effective.
That said ….
Notice I specifically said experienced resident hunter. That’s meant specifically and literally. Small calibers can be exceedingly good killers, but they don’t stop worth a damn, and they don’t leave much of a blood trail. The main issue is margin of error, and as a visiting hunter, no matter how experienced, you don’t yet know what you don’t know, so eliminating your margin of error isn’t a very good idea . This site leans into bigger is better as a general rule, but hunting skill, prudence, and good shooting with quality bullets are still king.
If it were legal and my ph were willing, I’d hunt buffalo in open country with a .338 and quality 250 grain bullets without hesitation.
btw, grand veneur in the previous post makes some excellent points.