To respond seriously to the original OP, I have killed 4 bulls, all with a .375 in three different rifles. I have been around the taking of several others. Of mine, two were taken with a TSX and two with A-Frames. All were essentially one shot kills, with the animal down within twenty-yards. Two were given safety final shots.
As a client, I would not use a solid of any description for my first shot at a buffalo under any circumstances. Frankly, I would not use one at all, I do not care what my PH suggested, but you should follow his guidance. Were I headed out tomorrow morning, my rifle (a .375) would be fully loaded with A Frames.
I will not use a fragmenting or petal shedding bullet on a whitetail, much less a cape buffalo and would be stunned if any PH would think that was a good idea.
The actual lesson I would take very much to heart from the incident with Greg Michelson is shot placement. As a client, we really have only one responsibility in approaching a buffalo - put the first shot, with a quality bullet, exactly where it needs to go. Do that and everyone goes home to celebrate the conclusion of a great hunt. Screw that first shot up, and a client may have the opportunity to deal with a very unpleasant what should have been for the rest of his life while a PH's or Tracker's family deals with much more.
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@375Fox, I pray no PH ever packs along a drone on one of my hunts.