So checked with national parks guys I know. They used FN military issue rifles- full auto but set to semi auto for all of the smaller else. They used standard military issue ammo- not armor piercing. They used 458 win mag on bulls. Chris commented that art alphins rounds were the first monolithics they had seen but he doesn’t recall the weight. He said the 458’s were a mixed bag - bsa, Winchester and FN from what he can recall. There may also have been private rifles used but on a national parks salary, I would guess they used the issue rifles as much as possible. So the humble 308 probably dispatched more elephant than any other cartridge and the 458 win mag more than all the ‘proper’ cartridges !