So why do bullets sometimes appear to “knock down” an animal? Most of the time this occurs because the animal was hit in the spine. It isn’t knocked down, but falls down because the spinal cord is severed. Sometimes, however, a bullet passes close enough to the spine to temporarily disrupt the nervous system, often by striking a rib or the “dorsal processes” on top of the vertebrae. If the bullet passes under the spine, through the lungs, the deer probably will go down and stay down, but if the bullet hits the top of the spine the deer may get up and run away.

A related theory is that a bullet that stays inside a deer expends all its energy, thus somehow “shocking” the deer more severely. Well, not exactly. Bullets that stay inside usually do so because they expanded widely. This slows them down quickly, due to resistance—but the wider bullet also creates a bigger hole in the deer’s vital organs. The bigger hole, not kinetic energy shocking the deer, kills quickly.

How much energy is “lost” when a bullet exits? This has been determined by setting up a chronograph on the far side of a block of media. Normally an exiting bullet is going less than 1000 fps—often less—and we can assume the same is true of a bullet that exits a deer. A 180-grain bullet from a .30-’06 Sprg. at 100 yards carries about 2,500 ft.-lbs. of kinetic energy. If the bullet retains two-thirds of its weight (120 grains) and exits at 1000 fps , it has 266 ft.-lbs. of energy. Subtract 266 from 2,500 and we find that more than 2,200 ft.-lbs. of energy was “dumped” inside the animal. This would seem to be sufficient.

This is also part of the reason why many bullets are found just under the hide on the far side of big-game animals. Fresh animal hide is fairly tough, somewhat elastic, and only lightly connected to the muscle underneath. Most expanded bullets are rounded into the classic lead-faced “mushroom,” so they can’t cut their way through the hide at vastly reduced velocity. Instead they tend to push the hide away from the muscle—until the hide stops stretching and snaps back.

This is the heart of another fallacy believed even by some experienced hunters, who reason that a bullet that doesn’t exit on broadside shots might not penetrate deeply enough on angling shots. This sounds logical, except that the inside of an animal’s chest is mostly lungs, the softest organs in an animal’s body, since they’re filled partly with air. A bullet that penetrates into the lungs will almost always keep going until it reaches something tougher.

My wife Eileen shot a Shiras moose as it quartered away at about 125 yards. The Partition entered the short ribs on the left side and ended up under the hide on the right shoulder, with more than 30 inches of penetration. It did not stop halfway there, even though we have found other 150-grain Partitions under the hide after they only penetrated 15 inches of broadside elk.

Some modern bullets open into four sharp “petals” rather than a rounded mushroom. These petals tend to cut through the hide instead of merely pushing, one reason bullets like the Barnes X-Bullet and Nosler E-Tip often exit.

Of course, X-Bullets and E-Tips retain more weight than most bullets, but many bullets that retain 90 percent of their weight don’t penetrate nearly as deeply. Frontal area is the primary factor in penetration, not retained weight. I once watched a hunting buddy shoot a 100-pound fallow deer with a 360-gr.ain.416 Woodleigh bullet, and the bullet stayed in the little deer. It was shot from a .416 wildcat at close to 2700 fps, somewhat faster than the muzzle velocity the bullet was designed for. It opened up to two and a half times its original diameter, so it didn’t penetrate very far even though it retained 90 percent of its weight.

Oh, and the big bullet did not knock the deer down, despite striking with over “two tons” of kinetic energy. Instead the deer stumbled a few yards before falling. It takes at least 10 seconds for blood pressure to drop after even a small “big-game” animal is hit in the chest, even with a heavy bullet. Expanding bullets work because they induce the medical kind of “shock,” causing blood pressure to drop by putting a hole in the vitals.

In the end it’s that simple.