I started using Nosler Partitions for Elk size animals in the late 70's when I had my .30-06 converted to a .30 Gibbs. With the increased velocity of the Gibbs, I wanted (and got) deeper penetration with the Partitions than with the standard cup and core bullets. This combination worked great for almost 30 years giving me mostly one shot kills on 22 elk, 2 moose, an Alaskan caribou, and a mountain goat.
I've never made a big deal about recovering the bullet from the animals that I've shot. If I find it fine, if I don't, fine. On North American animals, I try to shoot into the crease behind the front leg. I only shot 180 gr Partitions as hunting bullets in my .30 Gibbs. The Partitions that I did find were usually just under the skin on the opposite side of the bull.
This photo shows .30 caliber 180 gr Nosler Partitions that I have recovered from elk that I shot. They all expanded back to the copper center to about twice their caliber diameter, and the lead core from the front half was gone.
In 2005 I booked a Cape Buffalo hunt in Zimbabwe. I built a .375 Rem Ultra Mag rifle for that hunt. I had heard alot about Barnes bullets, so new rifle, new bullets. I worked up a load with 300 gr TSX bullets that gave me 3-shot MOA groups at 2850 fps. This combination gave me a one shot kill on my Cape Buffalo and four plains game animals in Zimbabwe and South Africa. The only bullet that I recovered was from the Cape Buffalo. It was in the shoulder opposite from the entrance, and it expanded to the advertized Barnes mushroom.
I hunted the Eastern Cape region of South Africa in 2007, and the only rifle that I took was my .375 RUM. For this hunt I wanted a flatter shooting bullet than the 300 gr TSX, so I worked up a load with the Barnes 270 gr TSX. This load also shoots 3-shot MOA groups on paper to 300 yds at a muzzle velocity of 3043 fps. On this hunt I shot 14 animals varying in size from Steinbok to a Cape Eland. I only recovered two bullets from the animals that I shot. Both were from a Kudu bull that I shot just before sundown.
At my first shot the bull was quarting toward me at 165 yds. The bullet entered the front of his left shoulder and stopped under the skin on the back of his right ham. This bullet expanded to the classic Barnes mushroom, but broke off one petal. After my first shot, the bull ran a few yards and stopped broad side. Since it was so close to sundown, I put a second shot in him. The second bullet entered his left shoulder and stopped just under the skin of his right shoulder. It expanded to the classic Barnes mushroom.
This photo shows the Barnes TSX bullets that I recovered from my Cape Buffalo and Cape Kudu. They all expanded to twice their caliber diameter (0.75-0.81").
My experience with Barnes bullets is limited to 19 African animals. I only recovered 3 bullets and they expanded to a classic double caliber diameter mushroom. Two of them retained 100% of their original weight. All of the animals except two died within 50 yds of where they were shot. The two that didn't were shot too far back with the first shot (shooter error) and had to be chased and shot again.
I am currently working on a 180 gr TSX load for my new .300 Weatherby for elk and larger animals.