I have only shot one moose in my time hunting so far. I was shooting my 7mm AM loaded with a 160 gr Accubond loaded to 3400 fps. The bull was at 150 yards on the first shot which was just behind the shoulder broadside. The bull flinched a bit and started walking with no sign of reaction. Second shot was again through both lungs, with no sign of hit at all other then knocking the dust off him.
Third shot was after a decent wait and I pinned both shoulders and be fell on his nose. We gave him 15 minutes and walked up to him. He was still alive and needed a finisher. Was this bullet failure, hardly. Both shots through the lungs stopped just under the hide on the off side. The shot through both shoulders was found stopped just past the offside shoulder bone in the shoulder meat.
Tissue damage, perfect. There as a fist diameter wound channel with both rounds through the lungs. It was straight and consistant on both lots of damage. Same with the shoulder hit but not as dramatic through the chest cavity.
I was perfectly happy with the bullets performance. What surprised me was how slow the metabolism of these animals is. That and they have HUGE lung capacity, HUGE blood supply and very low metabolism. This adds up to them being able to take serious amounts of vital damage and still it takes them a lot of time to actually die.
Now, from what I have heard, moose are not terribly tough like a bull elk can be to put down or a full rut whitetail can be from time to time to kill. Moose seem to hurt easily but can be a pain to kill, or at least can take some time to kill quickly. Like everything, some fall on their nose at the first shot, some do not, it should not be expected.
Three shots to kill a big moose does not sound terrible to me personally. Especially when most of us will keep shooting as quickly as possible on heavier game just to do as much damage to the vitals as possible in the short time we have when shooting at big game.
Personally, the choice to go with the 250 gr is a poor decision as likely the 300 gr at Lapua velocities would have performed perfectly.
For water buff, I assume this we are not talking Asianic and not cape buffalo. If Cape, Not sure where its even legal to hunt them with a 338 but I am sure it is somewhere. If I were to do that or have a customer come to me asking for my opinion on which bullet to use it would be the 285 gr Barnes TSX or the 270 gr Swift A-Frame.
There comes a time when you have to chose between long range performance and big game stopping performance. If you want to combine the two, its a good idea to step up in caliber. At long range on heavy game, even the mighty 338 Lapua is not excessively powerful.
Still, if the 338 Lapua was the chambering being used, I would start with one of the above bullets. After seeing recently what a bullet with a BC of .425 did at slightly over 1000 yards, I think one would be much better off getting a bullet that WILL get the job done no matter what, then test it and learn what it will and will not do at longer ranges. The results will be much better that way. Again, its difficult to get ONE bullet that will expand well at long range, soft impacts as well as hold together and penetrate well on close range, high velocity, hard impacts.
To get this, there are compromises that have to be made. Anytime there is a compromise, there is an OPPORTUNITY, for something to happen that someone could describe as a failure when in fact it really is not.
On heavy game, prepare for the close range hard impact and make due at longer ranges. This may mean you give up some extreme range distance with the combo but the alternative is far less acceptable.