I finally got curious enough to look at my hunting notes, which go back to the mid-1970's, to see which bullet/cartridge combinations dropped whitetails at impact with "pure" chest shots, meaning no bone was struck other than ribs. The list is an interesting one, partly because not one whitetail dropped at impact from a pure chest shot from a .243. But none of the bullets used in the .243 was an 85-grain Sierra HPBT GameKing.
However, at least half my hunting, and a good portion of my wife's, takes place here in Montana, where there's often a chance of running into an elk. So we tend to use slightly larger and stouter bullets than 85-grain 6mm's. The smallest cartridge/bullet combination that dropped many whitetails right there was the .270 Winchester with 130-grain Nosler Partitions, and the largest the .338 Winchester Magnum with 200-grain bullets, either Speer Hot-Cores or Nosler Ballistic Tips or AccuBonds. Some 7mm and .30 caliber loads did the job too, mostly using Ballistic Tips, AccuBonds or other bullets designed to lose some weight.
The ONLY animal shot with any sort of super weight-retaining bullet that I can recall dropping on impact as the result of a pure chest shot was a pronghorn doe killed at around 300 yards with a .257 Roberts Ackley Improved and a 100-grain XLC, the blue-coated version of the X-Bullet Barnes made for a while before the TSX solved the fouling/accuracy problems. The bullet started at around 3350 fps, and landed high in the lungs.
Have also seen some animals other that whitetails dropped right there with the standard .257 Roberts, the most common bullet the 115-grain Nosler Partition. In fact a 115 Partition has done the trick at ranges from about 100 yards (a feral boar in Texas weighing around 175 pounds) to 275 yards on a Wyoming pronghorn buck.
But if I were going to pick one bullet for dropping whitetails quickly with pure chest shots it would probably be a Berger--and for the same reason the .243 apparently does the job with 85 Sierras--massive internal damage. Have seen a higher percentage of animals dropped right there with Bergers than any other bullet, ranging in size from around 75 pounds to 400+ on the hoof.
While relatively few were whitetails (for the reason mentioned above--most but not all of our whitetail hunting is done in Montana), some were other deer, or feral goats of about the same size--and goats are far tougher than any of the several species of deer Eillen and I have hunted.
Unlike most expanding bullets, the Bergers also have the virtue of penetrating a couple of inches before starting to open, which not only ruins far less meat around the entrance hole, but on deer-sized game insures that the bullet penetrates sufficently into the chest. They penetrate the same way on the shoulder bones of deer-sized game, or at least they have on the several dozen animals I've seen taken with them.
Here I must also mention something nobody else has discussed: Whitetails vary considerably over their range in North America. Here in Montana a mature doe will be about the same size as mature bucks in southern Texas, and I've shot mature does on culls in Texas that were the size of Montana fawns. A mature Montana buck will weigh around 200 pounds, or if from farm country even field-dress more than 200. Bucks from the Midwest and southern Canada tend to be even larger. On a hunt in Manitoba a friend killed a forkhorn whitetail field-dressing over 200. Body size does matter, and what will instantly drop a whitetail weighing 100 pounds on the hoof probably won't do the same to bucks weighing 200-300 pounds.
The one constant I've seen, however, is bullets retaining all or most of their weight rarely drop them right there with pure chest shots. Instead they've dropped most consistently to bullets losing some or most of their weight, and with bullets like Nosler Partitions a muzzle velocity of at least around 3000 fps definitely makes a difference.
