I've seen a number of buffalo killed with Nosler Partitions, from 300-grain .375's to 500-grain .458's. They work fine, and in fact on average penetrate at least as deeply as A-Frames of the same weight and diameter.
This is partly because all Nosler Partitions above .35 caliber have the partition placed further forward than smaller-caliber models, resulting in higher weight retention. The .375 and .416 Partitions recovered from buffalo average 88.6% weight retention, but the rear end doesn't expand as it often does with A-Frames. Instead it stays cylindrical, so penetration is often deeper than with A-Frames.
The rear-end expansion in A-Frames is due to the rear core not being bonded like the front core. It usually occurs when the bullet hits heavier bone, or when impact velocity is pretty high. The last isn't common on buffalo, but heavy bone is. This doesn't mean A-Frames don't work well. They do, but they don't penetrate any deeper than buffalo-sized Nosler Partitions.
I haven't seen any 500-grain .458 Noslers recovered from buffalo, though one did stay inside a bull my hunting partner shot with a .458 Lott. The bull was facing us, head up, at about 40 yards, and my friend put the bullet in the center of its neck. The bull collapsed and never moved. The bullet broke the spine and ended up somewhere in the guts, where it wasn't found.
Usually 400-grain .416's exit on broadside shots, unless shoulder bone is encountered, whereupon they end up under the hide on the far side. I once shot a Botswana bull angling away to the left with a 400 from a .416 Rigby. The bullet went through the front of the paunch and both lungs before ending up in the right shoulder, around six feet of penetration. 300-grain .375's usually stop under the hide on the far side with broadside shots, which some PH's prefer when hunting in herds, to avoid the bullet going on through and wounding another buffalo.
Nosler adjusts the forward placement of the Partition considerably from the smallest to the largest. The lighter Partitions, which are often used on deer-sized game, are designed to retain less weight, to provide quicker kills on lighter game from the fragmentation of the front core. The least amount of retained weight of any recovered Partition in my collection is 54%. That was a 150-grain .270 recovered from the Shiras moose my wife killed in 1989--which still penetrated from the left rear of the ribs to the bull's right shoulder. (The bull took 1-1/2 steps before collapsing.)
Many bullet companies make similar "adjustments" in their big game bullets, according to the size of the game most of those bullets will be used on. Aside from the obvious, such as jacket thickness, they also adjust core hardness or jacket taper. Which is why it's often a mistake to assume ALL bullets of a certain make will perform the same when they hit big game.
