Other than my first deer and ellk hunts 50 some years ago, I've always hunted with my own rifles.
I went on my first Cape Buffalo hunt in 2005, and for that hunt I built a .375 RUM in a Remington 700 action. I've always been a reloader, so for that hunt I worked up a hunting load with 300 gr Barnes TSX bullets, and a practice load with 300 gr Sierra GameKing bullets.
I also worked up a very low kicking practice load with cast bullets. The only probllem with those is that the point of impact is very different than the poi of the full power loads, so I have to re-zero each time I switch bullets.
The second time that I took my .375 RUM to Africa it was only a Plains Game hunt, using 275 gr TSX bullets. They worked fine on animals down to the size of Steenboks and a Vaal Rhebok.
On my last African hunt, in Mozambique, there was another hunter in camp that had booked a Leopard and Sable hunt. He talked big about how good his rifles at home were out to 600 yds, but he didn't bring his own rifle on that hunt, electing to use the Outfitter's camp rifles.
When he first shot the Outfitters .375 H&H, they discovered that the scope was loose, and no-one in camp had a tool to fix it. So he was left with the Outfitters .30-06 and he didn't like it. After listening to him wine for a couple of days, I agreed to let him use my .300 Weatherby if we saw a good bull close to the truck.
When we did see a good Sable bull, it took off through the brush. We took off after it, and this other hunter used my rifle, that I had spent over 80 hours finishing and checkering the Fancy walnut stock, to push the brush away in front of him. We didn't catch up to that Sable, and when we got back to the truck, he handed my rifle back to me...with a shell in the chamber and the safety off.
The next morning when we got back into the truck, one of the scouts asked if he should bring the camp .30-06. This other hunter said "Why" and I replied "So you have a rifle to hunt with."