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Expanding Bullets: How They Really Work

There are many myths and misconceptions when it comes to what hunting bullets actually do—or don’t do—when impacting game.


Back when I was a college student who spent as much time hunting and fishing as attending class at the University of Montana, one of my hunting mentors told me not to use my .270 Win. “The .270 is too fast for timber huntin’. The bullets zip right through before they can open up!” I knew there was something screwy about this theory, but I didn’t dare argue with it.

Today, of course, sophisticated hunters know that some bullets open up faster than others, the reason some bullets are more effective on prairie dogs and others more effective on elk. These hunters are just as wrong as my old elk-hunting buddy. The truth is that almost all hunting bullets expand completely by the time they penetrate their own length. This has been proven by high-speed photography and by ballistic media that retain the shape of the hole created by the bullet’s impact. The biggest hole made by a typical hunting bullet is immediately after it enters, not several inches beyond. Some hunters might argue that various ballistic media aren’t “reality.” C’mon, guys. Most meat damage on a deer occurs around the entrance hole, not on the far side of the animal.

It’s true that some bullets expand less violently than others. This can create the impression that they’re opening more slowly, but the difference lies in how much the bullet fragments upon expanding. The clearest example of this is the “varmint” bullet that disintegrates in order to kill small pests instantaneously. At the other extreme is a heavy-duty, big-game bullet designed to retain most of its weight. The first creates a huge hole immediately upon impact. The second makes a smaller hole upon impact, then continues onward, creating a narrow, long “wound channel.”

Big-game bullets often punch through the hide on the far side, sometimes leaving an exit hole not much bigger than the entrance hole. Many hunters take this small exit hole as evidence that the bullet didn’t expand at all—which makes me wonder if they actually field-dress the animals they shoot, since damage inside the chest makes it obvious the bullet expanded.

I first became suspicious about the “slow-expanding” bullet theory about a decade ago when using a High Wall single-shot rifle in .30-40 Krag to shoot prairie dogs. I’d planned to hunt deer with that rifle, using a tang-mounted rear aperture and gold bead front sight, so I took it prairie dogging with some 180-grain Winchester Power-Point handloads. My companions found this amusing until just before noon when a prairie dog stood up around 200 yards away. I held the top of the bead on the varmint and shot. It tipped over, and when we investigated we found a small hole in its chest where the bullet had entered—and a 3/4-inch hole in its back, where the expanded bullet had exited. The reason the animal didn’t come apart like those shot with .22-.250 Rems. is that the tougher bullet from the .30-40 didn’t disintegrateᰬbut it still expanded, and obviously quickly.

There’s one exception to this bullet behavior, the Berger Very Low Drag (VLD) bullet. Several years ago a few hunters started using these thin-jacket, soft-core “target” bullets to hunt deer and other big game. The VLDs did not disintegrate immediately upon striking animals, but inside them. In fact their entrance hole looked like it was poked by a knitting needle. How could this be?

Hunting bullets expand because their front end is weakened. Sometimes this is accomplished with a hole in the front end (making a “hollow-point”) and sometimes by leaving the lead core exposed (“soft-point”). Both can be further weakened by longitudinal cuts. The front end collapses outward (“mushrooms”) when the bullet strikes an animal.

In theory a hollow-point bullet opens when the cavity is forced wider by fluid or flesh. I am not so sure about this, because my favorite “tough” bullet test is a stack of dry newspapers. Even relatively hard hollow-points like Barnes X-Bullets will open up in fluid-free newspaper.

Also, I’ve tried poking the tip of a small safety pin into the hollow-point of a 168-grain 7 mm VLD and the pin simply stopped. In effect there is no hole in the tip of a VLD. The jacket, however, is extremely thin, and the tip of the bullet extends beyond the lead core, so the tip itself is hollow. Apparently the long, sharp ogive allows a VLD to pierce the hide, plus an inch or two of tissue beyond it, before the thin jacket collapses and the bullet upsets violently. This has since been demonstrated thousands of times not only in test media but game animals. In fact it normally works even when the bullet impacts light bone. The Berger VLD is among the quickest-killing deer bullets around because it disintegrates inside an animal, opening more slowly than standard big-game bullets.

The odd thing is that Berger recently introduced a heavier-jacket version, though not for hunting. In some target rifles the original, thin-jacketed version didn’t hold up, especially when shot from cut-rifled barrels. So the thick-jacket version of the VLD is the “target” bullet, and the thin-jacket VLD the “hunting” bullet. Obviously this goes against the “rules” of big-game bullet behavior that every hunter knows.

This isn’t because the hunter in question has actually studied the subject, but because he heard stuff ’round the campfire or read it in magazines. Among other things, he’s been told that “shock” is a major factor in how expanding bullets work. When asked to explain shock the hunter in question often becomes irate, and responds with, “Everybody knows what shock is!” Maybe, maybe not. Let’s look up shock in an unabridged descendant of Noah Webster’s dictionary. It turns out there are a bunch of shocks, including sheaves of grain, the physiological effect of an electric current and being startled, as in “the rebuke came as a shock.” Obviously those don’t apply, since hunters don’t zap deer with 110 AC, slap them with a wheat-whip, or rebuke them into the freezer. The definitions that could apply are:

  • 1.) A sudden and violent blow or impact; collision.

  • 2.) Pathology: A collapse of circulatory function, caused by severe injury, blood loss, or disease, and characterized by pallor, sweating, weak pulse and very low blood pressure.

Many hunters take the first definition. They think that a bullet hits so hard that a deer is shocked into unconsciousness, like a movie bad guy being lifted off his feet by a shotgun blast. Often kinetic energy is quoted, as in “the bullet hit with 2,000 ft.-lbs. of force.” Sometimes this is even turned into “a ton of energy,” conjuring images of a Hollywood car chase.

This sounds good, but a 2,000-pound compact car going 60 m.p.h. (88 fps) develops around 240,000 ft.-lbs. of kinetic energy, almost 100 times as much energy as a 180-grain .30-’06 Sprg. bullet retains at 100 yards. The car’s energy will lift a deer off its feet, but the bullet won’t.

In fact if a rifle bullet developed 240,000 ft.-lbs. of muzzle energy the rifle would slam its shooter to the ground, since the average hunter is about the same size as a mature whitetail buck. This is because of an old Newtonian rule of physics: Every action has an equal and opposite reaction. This is what we feel when a .30-’06 Sprg. recoils, the “equal and opposite reaction” to the bullet leaving the muzzle.

Actually our shoulder feels a little more than that, because part of a rifle’s recoil is the rocket effect of hot powder gas leaving the muzzle—which the deer doesn’t receive. Yet when firing a .30-’06 Sprg. we’re not slammed to the ground; instead our shoulder is pushed back an inch or two.

To demonstrate this lack of knock-down power I once built a “deer” out of a 3-foot-long wooden box and some 2x4s. When the box was filled with moist earth the deer weighed 150 pounds. I shot into the broadside box from 100 yards away, starting with .223 Rem., then .257 Roberts, .30-’06 Sprg., .338 Win. Mag. and, finally, the .416 Rem. Mag. The bullets were all stopped by the fake deer. The .416 seemed to rock the box a little, but the others didn’t move it, even slightly.

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12 Responses to Expanding Bullets: How They Really Work

zigo wrote:
December 10, 2012

you are correct about most of what you say but,There still is a shock value involved, but it is the reaction of the soft tissue being extremely damaged . the faster a bullet is traveling,the higher degree of damage is involved to the soft tissue,nerve endings by the blood displacing at a higher velocity. if you were to take a water bottle shoot through it at a low velocity, the water would simply move out of the way of the bullet,as the velocity increases,the water does not have time to move out of the way, damaging any tissue that can not with stand the rapid expansion, causing massive damage and instant death.that's why many times a deer is shot through the chest,without hitting the spinal cord,causes instant death.

ntrudr800 wrote:
July 16, 2011

Interesting & useful article

Rob wrote:
November 21, 2010

I figured this out years ago. Common sense told me that a piece of lead less than a 1/2" inch in diameter couldn't knock me down no matter how fast it was going. And I was pretty sure that if it was going too fast it would probably zip right through me without transferring all of it's energy making it even more ineffective. My favorite round for nearly everything I hunt from antelope to elk is a 7mm Remington Mag with a 140 grain softpoitn running out at about 3,200 fps. Accurate bullet placement is everything.

Eric wrote:
November 16, 2010

I once shot an approximately 120lbs doe with a .300 Win Mag loaded with 150gr soft points at 3300-3400fps. Shot her right through the rib cage behind the shoulder. There was at least a 2 inch exit hole with pieces of lung scattered in a triangle shaped pattern just beyond the exit wound. Deer literally flipped over in her tracks without moving following the shot. When field dressed the lungs were shredded and the heart literally fell out of the chest cavity having been completely sheared away from the great vessels. I think there is definitely something to the hydrostatic shock theory.

Rifleman wrote:
November 16, 2010

Building a box, filling it with moist dirt and then extrapolating transfer of projectile energy to animal flesh and bone is like comparing a child's riding his tricycle down the sidewalk to an F-18 Super Hornet on an attack run because they both move through air. How does Barsness spell b.a.l.l.i.s.t.i.c g.e.l.a.t.i.n? Perhaps some insights from African P.H.s who understand what it takes to anchor any of the Big Five might have lent some practical legitimacy to this article.

Jim from Missouri wrote:
November 16, 2010

MY son and I kill a lot of whitetail deer. He hunts with a 338 win mag and I use a 375 h&h mag just because we like those guns. We dress and cut up our own deer. We try to shoot the deer just behind the front shoulder with a broadside shot. With either gun, we will have a nice entrance hole and a slightly larger exit hole with the vitals pulvurized. If the bullet goes too high or too far forward and strikes connected bone we end up with a large exit wound. As large as 12 in. By the way, you can't tell the difference from the 338 and the 375. He shots speer 250 gr grand slam and I shoot 300 gr Hornady rn. I always thought it had someting to do with the bullet slowing down for an instant that made the difference somehow. I enjoyed your article, but I'll have to re read it several times to maybe get my answer. I think it's in there somewhere.

Anton Petrash wrote:
November 16, 2010

The problem with hydrostatic shock tearing open the internal organs is the extreme elasticity of these tissues. The water jugs, while not entirely rigid, are not very elastic, and therefor are torn apart.

sunaj wrote:
November 16, 2010

Useful article, but the explanation of shock was not explained very well, in a living system the effect of hydrostatic pressure cause an instantaneuos pressure wave that destroys tissue, function and disables the nervous system, hence it frequently stops the animal immediately

Anton Petrash wrote:
November 16, 2010

It's time to put and end to the idea that "muzzle" or kinetic energy is what causes bullet penetration and that anything other than shot placement and penetration depth contribute to "knock down power." Essentially, momentum (F=ma) and not kinetic energy (F=mv2)is the important force here. That's why I prefer big subsonic rounds (.45 230gr and 9mm 147grain) for self-defense.

Rancher wrote:
November 16, 2010

I agree for the most part, however I question a couple of things based on my experience/observations. The long narrow wound channel of the hunting bullet may be true but I suggest as Pop did that the amount of hydrostatic shock damage around that wound channel is what determines the lethality. Also regarding the meat damage around entrance vs exit, I often see more damage around the exit. It appears to me to be for 2 reasons. 1. The bullet does not fully expand instantly on entrance. 2. Exit damage is the result of the expanded bullet as well as the blood and tissue it is pushing (hydrostatic shock)

Pop wrote:
November 12, 2010

Very interesting and makes alot of sense. But... When I was a kid, "shock" was explained to me as "hydrostatic shock". I.e. When you hit a one gallon water jug with a hegh velocity bullet the water jug exploddes. It explodes because the bullet slamming into water, at very high speed,creates a wave of high pressure which shatters the jug with a momentary pulse of very high water pressure. When a bullet hits the inside of the animal "hydrostatic shiock" tears open the enternal organs. So I was taught. What do you think blows up the jug? Is there a "hydrostatic shock effect" that streaches and tears the internal organs? You believe this because?

Joe Gallagher wrote:
November 10, 2010

Great article!!!