After analyzing my big game hunting notes (now coming up on 50 years of dead stuff), I decided the common knowledge that boattail cup-and-cores come apart far more frequently than flat bases was a little exaggerated, since an equal number of flat-base bullets had separated over that period, both in my rifles and those of hunting companions. Also, even though some cores left the jacket, the bullet almost always killed the animal anyway. Often the "separated" core was found in or next to the jacket under the hide on the far side.
But one of the very few bullets that failed to penetrate the chest cavity of a deer was a Hornady boattail Interlock. It wasn't the 100-grain 6mm, but the 117-grain .25. The rifle was a .257 Roberts and the animal a mule deer doe about 100 uards away, quartering toward my cousin Eric, who was standing next to me. The logical shot was the shoulder joint, and that's where the bullet went. The deer turned and started hobbling away, and Eric put another in the ribs, finishing the job. The remains of the first bullet hadn't penetrated the ribs.
Of course, saw basically the same thing on a forkhorn mule deer shot with a 150-grain Winchester Silvertip from a .30-06 factory load. (It was the original Silvertip, not the Ballistic Silvertip, which is a different-colored Nosler BT.) The range there was about 200 yards, and again the bullet hit the shoulder joint and came apart. I found the empty jacket resting against the ribs. It happened another time with a 150-grain Federal .30-30 factory load on a Montana whitetail doe, which supposedly isn't possible at such low velocity.
On the other hand, have had a Sierra 120 6.5mm at about 2700 and a Nosler Ballistic Tip 100 .25 at 3000 go through shoulder joints on deer of about the same size and end up at the rear of the ribs on the other side. The Sierra shot placement was a little bit of an accident, as the deer turned a little just as I shot, but the BT was deliberate, and the range only about 50 yards. That little 100-grain Ballistic Tip has a pretty thick jacket.
I was kind of surprised at the 117 Hornady not making it through the ribs, and really surprised at the 150 .30-30 bullet, but then life is full of surprises.
