Check out accuratereloading they have a wealth of knowlege on african hunting both plains and buff, I just read a post the other day about charging buff, the owner of the site, Saeed, said that he's taken over a 100 buff and never had a charge, he shoots realoads in a wildcat with "home made" bullets much like a X bullet...
From what I understand about 75% of the buff taken in recent years are shot with well constructed "soft" points, i.e. A Frames, Barnes X, Failsafes, Partitions, Woodliegh, etc... But there are still some guys that will only shoot solids. One hole in one hole out, for a better blood trail, but the kill isn't quite as quick. I'm pretty sure a 400 grain soft point is going to break the fore shoulder... I woudn't worry about reloads and haveing a "dud", I've had duds with factory ammo... Your life really isn't going to be in that much danger. Very, very, few clients have ever been run into the ground and killed, for the most part the goreings that happen each year are on PH's and locals.
The chance of you actually being charged are about nil anyway, as from what I understand most every time the buff will run off after being shot. Sure there is a chance he could turn, but the odds of YOU actually having a cool head, and having proficency with your weapon to kill a charging buff at 25 yards while trying to sort him out in your scope (if you have one) is probably pretty slim. I mean no offence, but I really doubt that you've had enough practice to need to worry about that anyway. I shoot a lot and I know I couldn't come close to passing the test with a big bore, much less a 22... Do a quick serch on the proficency test that PH's have to pass and ask yourself if you think you could pass, and then go try it...
You're PH is there to sort things out if they happen to go wrong thats his job, not yours as a client, if it was, we wouldn't need them would we? He'll be packing the true "stopper" if one needs to be dropped. Personally if it was me and I was really worried about needing a stopper, I'd get a Lott or a 470 NE... and leave that little "pee shooter" at home...
My guess is that if you ask your PH he'll tell you that you should worry about putting that first shot where it counts and let him worry about what happens next. Just ask him what he prefers you shoot in your gun, some like you to have a soft first shot and then solids in the mag, to pump into him as he runs off... More lead in the air is good...
I hope you have a great hunt and shoot a big ol duga. Where are you going and who are you going with?