While most game expires from bullet wounds due to hemorrhaging, shocking bullet performance sometimes drops it like a bolt of lightning.

Such a shocking event happened in front of my .30-30 Winchester M94 way back in 1968. A whitetail “button buck” dashed past about 50 yards out. I swung and shot. It dropped in mid-leap, never to stir again.

Whenever I see something like this, I assume my bullet struck the animal’s central nervous system. But every now and then a post-mortem reveals a lung, heart, or even kidney strike. Such was the case with that deer. The 150-grain flat-nose had smacked it in the central chest cavity. I know there might be a leg bone connected to a hip bone, a hip bone connected to a back bone, and a back bone connected to a head bone—but there’s no lung bone connected to anything. Why does any shot to the chest sometimes result in instant death when the central nervous system wasn’t touched?

Shock. At least that’s what’s been claimed these past 70 years or so. “Hydrostatic shock” or “hydraulic pressure shock” are other names for the phenomenon. The bullet transmits its energy to the animal’s blood, tissues, and bones, sending high pressure waves to various organs, including the central nervous system, i.e. brain. Lights out.

Weatherby magnum cartridges have been famous for doing this. Roy Weatherby didn’t coin the “shock” theory, but he did a brisk business around it. Weatherby sold big rifles and big cartridges that sent bullets crashing into game at velocities so extravagant beasts collapsed as if unplugged. Sometimes.

Some basic rules of physics are at play here. If you double the mass of a projectile, you double its energy, but if you double its velocity, you quadruple its energy. At 3,300 fps, a 115-grain bullet from a .257 Weatherby Magnum, Roy’s favorite, is packing a heap of shock energy. So Weatherby was knocking at the right door. Yet his high-velocity cartridges didn’t and still don’t floor game fairly struck every time.


Big or small, Weatherby cartridges were designed to be fast. Roy apparently believed in the hydraulic shock effect.


In fact, game often runs off, merely wounded, leading legions of hunters to reject high-velocity cartridges and stick with big, slow bullets. (The Elmer Keith, Jack O’Connor feud.) The high-velocity, hydrostatic “shock” challenge is converting bullet energy into an effective destructive force every time, and bullet construction has a lot to do with that.

Most of us know that a solid bullet, the kind mandated for warfare but illegal for big-game hunting, zips through a body about like a target arrow. Regardless of its speed, it penetrates with precious little frontal area for transferring energy.  Enter the soft-nose, hollow-nose, expanding-nose, and breakaway-nose designs, all made to increase bullet area to damage more tissue and transfer more energy. But not too much. Excessive mushrooming leads to minimized penetration, as explained in this blog we published earlier.

This is why bullet makers swamp us with so many variations on the theme: soft lead, hard lead, thick jackets, tapered jackets, bonded jackets, sectioned and walled jackets, monolithic copper hollow points—they try various materials and constructions to control how much and how quickly hunting bullets expand and how much mass they retain for deep penetration.

One popular theory postulates that a bullet should expand just enough to maximize tissue contact but not so much that it passes through the animal. Thus, bullet energy is dumped inside the animal for maximum knockdown effect. The problem is, it doesn’t always work.

Part of the reason is variable impact velocity. A 150-grain projectile from a .30-378 Wby. Mag. at 100 yards hits a lot harder than the same bullet from a .308 Winchester. But at some distance downrange the .300 magnum slows to less than .30-30 velocity at ten yards. How do you build a bullet to handle all that?

Another part of the problem is where the bullet lands. Shoulder muscle and bone initiate a lot more friction and expansion than soft lung tissue. And a third problem is when the bullet strikes. One theory has it that a hit to the chest when the heart is beating and systolic pressure is peaking has the greatest hydraulic effect.

A fourth problem is the animal itself. Is it alert or sleepy? Healthy or weak? Active and agitated, high on adrenaline? Shot through the heart, one critter runs off, another merely continues browsing, and a third falls dead instantly.

Time and again I’ve shot game from 1,500-pound buffalo to 25-pound coyotes with bullets carrying anywhere from 1,500 to 5,000 foot-pounds of energy. Some of those bullets remained within the body cavity, dumping all their energy, yet the animals did not collapse as if unplugged. Other bullets passed through, yet the game did collapse. And vice versa.

Another hydraulic-shock issue is bloodshot meat. Whether the hydraulic pressure of a high velocity bullet kills instantly or not, it usually tears tissue and blows clotted blood far from the wound channel. Clearly, hydro-pressure is at work, and its not work that venison gourmands appreciate.

Whether you call this “knockdown power” or “hydrostatic shock,” you have to admit it surely isn’t consistent. So what’s going on?

In all honesty, I don’t know for certain, and I’m not certain anyone else does because there are strong arguments and evidence on both sides, including contradictory studies since 1947 on wounded soldiers as well as hogs and game animals as large as Cape buffalo. Some research has shown that “vascular pressure impulse” from a chest or abdomen hit can carry enough energy to damage nearby tissue the bullet doesn’t touch.

Watch videos of bullets passing through ballistic gelatin and you can see the temporary wound cavities in their wake. Slow-motion videos of animals at the time of bullet impact show dramatic contortions of the body as tissues flex, bulge, and absorb the energy. Energy waves are clearly making an impact. It can even reach from the thoracic cavity to the brain causing a precipitous rise in intercranial pressure. One study using EEG readings on the brains of pigs showed that a bullet strike as far back as the thigh caused neural and vascular damage in the brain.

Jim Carmichel once reported on a veterinarian-controlled study during a buffalo-culling operation in Africa. All buffalo were shot in the heart/lung. Some fell instantly; some did not. Post-mortem examinations revealed massive rupturing of brain blood vessels in those that collapsed at once. Those that didn’t collapse immediately showed no such rupturing. Sounds like good support for that systolic blood pressure idea. Anybody know how to time your shot for that?

This must have been what happened to my wife’s Mozambique buffalo shot with a Blaser R8 rifle spitting a 300-grain Barnes TSX. The bullet passed through the chest, broke no bones other than a rib, and lodged against the offside hide. When the herd thundered off, there lay the stricken bull—on its side, head up, glaring at us but unable to rise and charge. A mercy shot to the heart ended it.


This buffalo bull, shot through the chest (note the blood in its nostrils), suffered no broken bones, yet could not rise to charge. Did hydrostatic shock incapacitate it?


We didn’t autopsy the brain, but could there have been vascular brain damage from that first shot? What else explains the infamously aggressive Cape buffalo not rising to mayhem? All his limbs were intact.

Clearly, bullet shock works sometimes. But not all times. I’m guessing it’s much like that boxer’s punch. Sometimes what looks like a perfect, knockout punch barely fazes the opponent. Other times a Phantom Punch drops him in a heap à la Ali/Liston. The question is this: Do we want to trust to something that works well only sometimes?

The good news is we don’t have to. High velocity coupled with controlled-expansion bullets gives the best of both worlds. The hydrostatic force is delivered, but the bullet remains in one piece, expanded, to penetrate deep and physically damage vital organs. If hydrostatic pressure waves terminate the animal instantly, great. If not, hemorrhaging should. Of course, there remains the bloodshot-meat issue, but it can usually be avoided by shooting to miss major muscle groups.

Thankfully, each of us is free to hunt with big, slow bullets, small, fast bullets, or big, fast bullets. Regardless, we always have the responsibility to park those bullets in the right place. Accuracy uber alles.


For more from Ron Spomer, check out his website, ronspomeroutdoors.com, and be sure to subscribe to Sporting Classics for his rifles column and features.


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