I think Cape Buffalo is pushing it. Of course if it penetrates with selected shots it can kill. So can a .243 with good bullets and selected shots.

It's the non selected shots where more gun is needed. And when sub-standard cartridges are not good choices. In the high grass, thick close hurried shots in thick Jesse, the inevitable dangerous follow ups on a wounded beast. Then a .500 NE double rifle is desirable.

An advantage of an AR10 is the ability to fire lots of quick to make up for lack of knock down power.

IF we could have AR15s and AR10s and suppressors I would have a 5.56 with .300 Blackout barrels. An 8.6 might have some purpose?

But the 8.6 is very much a shorter range cartridge isn't it?