Heck I've killed Asian Water Buffalo with a .444 but according to the "experts" that is an impossibility. Was a remmington Corloc 240 grain, passed through the ribs, destroyed both lungs, recovered the perfectly intact, well mushroomed bullet in the skin on the off side.
FFiL,
That is an enlightening comment. I have a question what "expert" said that it is impossible to kill a large bovine with a .444? I am going to need a reference to where that has ever been said by a so called "expert".
I'd like to see a picture of your water buffalo where did you kill him? Was he a wild buffalo or a domestic one? Or did you kill him over in Australia or maybe South America?I know that there is a guy in Florida, Joe Bannon(sp?) that has a hunting operation for water buffalo I also have heard of several operations in various locations that provide "hunts" for Philippine buffalo but Joe is the only guy I know of who has hunts for true Asian sweepers. Are there other opportunities available? Was yours a sweeper or a short curled Philippine bull?
Now with regards to your bullet performance on your buff. You hit him in the softest vital area possible. You would have had very similar results with most any substantial caliber including a .308 or even a .270 or a 6.5 MM with a decent bullet. You even would have had a similar result if that Asian buff had been a cape buff.
NOW take that same bullet on that same animal and try to stop him as he is coming head on you might, MIGHT have got that bullet to the brain from a frontal presentation but it's doubtful. If you would have had to punch through the neck muscles into the heart or break a shoulder from a frontal angle you would have been completely and totally screwed! There is no way that bullet is going to punch through that much muscle and bone as Mr Jeff Cooper found out on a buffalo that he shot with his beloved .350 Rem Mag in the neck on a frontal shot with a quality soft point bullet. The slug was found about 8 inches deep in the massive neck muscle of the buff. The PH's .470 killed it.
Now on to the OP. Will a .338 Lapua reliably kill a cape buffalo or even an elephant with proper bullets. You bet it will. The various .338's have been doing it for years Don Allen of Dakota Arms killed several big buffalo with his .330 Dakota. With proper bullets they are quite capable of safely hunting and killing buffalo no two ways about it. Not so many years ago the .318 Accelerated Express was a highly regarded buffalo caliber. That round is essentially just a .30-06 necked up to a 8mm. Same goes for the multitudes of buffalo that have been killed with the .303 and the .333 Jeffery.
So why were these caliber restrictions put into place for thick skinned dangerous game? BTW thick skinned refers to buffalo, rhino, elephant and hippo and in some countries lion are grouped into the caliber restriction as well. Quite simply because the various game departments were getting tired of sending home the battered and mutilated remains of dead hunters who had been killed using these small bore weapons. And professional hunters and game cropping officers noticed that a larger bore with a minimum of .375 diameter using a sectional density of .300 or greater and producing a Fpe of 4,000 and better tended to reduce the number of coffins headed back home to Europe or America.
Once again the problem isn't killing the animal but rather stopping it in an emergency. I have no doubt that the .338 Lapua with a solid or premium 270 or 300 grain expanding bullet would be an adequate buffalo round.
However do not let the paper numbers make you into the next emergency air evac case. The .338 lacks diameter which makes it a marginal charge stopper. So does the .375 H&H IMO but it's the legal minimum. Hey you say "stick the bullet in the right spot and it doesn't matter" and that is true! But unless you've ever tried to stick a bullet in a buffaloes brain while it's charging and flinging it's head wildly I don't want to hear about it because it ain't that simple. And that is why we use a larger caliber that affords some margin of error.
So here's the crux....The law is the law and it was put into place with the hunters safety in mind. Until it's changed you can't use your .338 Lapua for hunting thick skinned DG in Africa. So if you are truly worried about it buy a .375 RUM instead it's pretty close to a .338 Lapua in power and it's DG legal. Problem solved.
PS
While Asian Water Buffalo are larger in size they simply do not have the explosive temperament of the African Cape Buffalo. There far far fewer injuries and deaths from water buffalo hunting that there are from cape buffalo hunting.