I meant to say that Karamojo Bell used a .275 and the widespread use of .30 cal. rifles among 'me-too' Europeans may have much to do with Bell and his use of lighter, high velocity ammo on heavy game like the elephants. The widespread availability of military ammo from the .303 to the 7.62 mm NATO and all of the Soviet stuff is what has driven choice among poorer locals hunting for the pot or insurgents looking for profit.
The .275 Rigby used by William David Maitland to take about 800 of his circa 1100 elephants is more commonly known as a 7x57 Mauser in U.S. cartridge designations. But Bell was no fool, and when starting out, himself used a Jeffrey dounle rifle on .450/400, certainly better suited for jumbo and rhino in brush. Note too that Bell's choice of 7mm ammunition was a full-jacketed pointed solid that would provide sufficient penetration to reach the brain, not always possible with some of the larger caliber weapons whose penetrative capabilities were a result of mass and weight rather than velocity and bullet design.
For most other beasties in Africa, the .375 so beloved by John *Pondoro* Taylor as an all-around African rifle will do the job, though something a bit more certain is preferanble for buffalo, though it will do fine on lions and other less massive beasties. Aside from the *big five* the American .30-06 and .308 Winchester will do just fine, and the .300 H&H or .300 Winchester Magnum will suffice about as well as the .338 Lapua Magnum or 9x54r, with the .375, .401 Rigby and similar equipment a step up from that- but the key is expert familiarity with the rifle and the knowledge of where to oplace the bullet, as Bell did.
I don't claim any great expertise, having only taken one elephant and three Nyati buffalo, back in the 1970s. But I believe if I were to return to hunt there again, assuming identical conditions, I'd go with a .450/400 double and a .338 boltrifle, with a .308 handy for cattle and any two-legged pests. And if elephant/rhino/buffalo were the only or primary reasons for the exercise, the .450/400 double and a .460 boltrifle would be just fine. And I wouldn't even feel terribly underequipped even with a .303 Enfield, which will do most anythihng a .308 can- which is quite a lot, actually.
But I'd be very picky about my choice of ammunition, and practice would extend to hundreds of rounds fired.
-archy-/-