Buckmasters Magazine

The Myth of Knockdown Power

The Myth of Knockdown Power

By Dave Henderson

Dropping a deer in its tracks is about shot placement, not bullet energy.

The two on left are the biggest, and they are both 147 yards,” said my hunting partner as he viewed a group of whitetails through a rangefinder as they fed at the edge of a Wyoming pasture.

With depredation permits in our pockets, the goal was venison rather than trophy racks, so the unsuspecting forkhorn buck and adult doe that had just been lasered were suitable targets.

A massive boulder provided a steady base and concealment as I placed the 150-yard aiming dot of the Nikon SlugHunter scope just behind the shoulder of the buck. Slow, deliberate pressure on the trigger released the sear at precisely 3.1 pounds.

The forkhorn collapsed immediately. After quickly cycling the shotgun, I swung the aiming circle to the doe’s shoulder and squeezed off another.

Down she went.

“Man, great shooting. You can’t argue with the knockdown power of that slug,” remarked my impressed hunting partner.

Actually, both statements were in error. When we went to the deer, both had been hit at the base of the neck — about 10 inches wide of where I’d been aiming. And it wasn’t the power of the slug that knocked the deer down, but rather the impact area.

Knockdown power, you see, is evident when you punch a hole somewhere important with a structurally sound projectile. It is the mechanical stress of the projectile crushing and cutting essential tissue and bone that causes the immediate collapse.

In other words, a deer falls over when something causes its brain or muscles to quit holding it up. Short-circuiting the central nervous system or a skeletal breakdown is the most immediate.

Shotgun blasts don’t propel bodies across rooms or through walls, contrary to what movies depict. But most hunters believe Hollywood.

If, after a shot, a hunter finds scurried tracks and a few drops of blood where he expected to see a pile of whitetail, he invariably decries the lack of knockdown power and embarks on a search for a more powerful load.

Most shop for knockdown power using muzzle energy as the standard and believe adding a sufficient number of foot-pounds will solve any problem.

Ask anyone which is more lethal — a round that produces 1,000 foot-pounds of energy or one that produces 3,000 foot-pounds — and they’ll side with the bigger load. I’m here to tell you that 1,000 foot-pounds, given the appropriate construction of the bullet, will knock down any animal immediately if it strikes the right spot, while the 3,000-pounder that misses the critical spot will not.

As a perceived expert on big-bore rifle and shotgun ammunition, I’m often approached for advice on loads with the most knockdown power. If I suggest that there is no such load and, in fact, that the energy of the load isn’t nearly as meaningful as shot placement, I’ve colored myself as ignorant.

I’ve heard touted the knockdown power of everything from the .204 Ruger (I’m not making this up) to .220 Swift to the expected magnums and 600-grain shotgun slugs. All such claims should be taken with an entire shaker of salt.

Of the nearly 200 head of big game animals I’ve taken over the last four-plus decades with centerfire and muzzleloading rifles, shotguns and handguns, maybe 10 percent dropped on the spot. In each case, it was due to a structural breakdown (neck, head or spine) or a hit that disrupted a vital function. None occurred from energy transfer — it simply doesn’t happen.

Energy alone will not drop an animal in its tracks. In fact, while energy is a factor in knockdown power, location of the hit and bullet construction are far more important.

In fact, how about if I told you that the whole idea of knockdown power related to kinetic energy is something that is impossible to achieve with a shoulder-fired shotgun or rifle?

Can we agree that Sir Isaac Newton knew a thing or two about physics? Well, his fabled musings that “for every action there is an opposite and equal reaction” implies that any load that is capable of flattening a deer on the spot will do the same thing to the shooter.

The Myth of Knockdown PowerThe difference is that since guns are heavier than bullets, we experience the forces in different ways, but Newton’s Third Law nevertheless applies.

Knocking down an animal in its tracks, you see, stems not from energy transfer but from damaging a body system enough for gravity to take over. The projectile has to disrupt one or more of the body’s major systems — nervous, circulatory or musculoskeletal — in order to knock it down.

In fact, it can be argued that velocity has a bigger effect on knockdown power than kinetic energy. Hydrostatic shock — the paralyzing virtual shock wave that runs through the body’s liquid mass, short-circuiting vital systems — is caused by a suitably constructed, high-velocity projectile.

Cavitations, or the destruction of residual tissue surrounding the actual wound channel, are caused by a sturdy, high-velocity projectile.

Note that hydrostatic shock and cavitations both result in the immediate disruption of vital functions or structural damage.

This is not to say that kinetic energy has no role in knockdown power. It does. An expanding bullet pushed at sufficient velocity will do this more effectively than one with less energy.

Simply citing kinetic energy (derived from the standard velocity-and-mass formula) ignores the abilities of the bullet. A bullet must accelerate negatively — ballistic jargon for the process of bullet expansion and slowing due to friction with tissue it is passing through.

Considering energy alone also ignores the ability of the bullet to fragment and cause multiple wound channels. These abilities are crucial characteristics of modern bullets and slugs and their ability to cause stress on tissue.

The construction of the bullet and its placement are far more critical to knockdown power than energy.

Understand that the concepts of knockdown power and killing power are not identical.

Energy is a far more important indicator of killing power than it is knockdown power. Cartridges that do not develop adequate energy are not likely to place very high on any rational killing power list.

Commercially, kinetic energy is the most commonly used measure of a load’s killing power. It is the figure listed, along with velocity, in practically all ballistic tables. It can be computed quite easily and is essentially the product of a bullet’s mass times its velocity squared.

Energy, the ability to do work (or damage in the case of a bullet or slug), is certainly an important component of killing power. It’s obvious that a bullet carrying more energy when it hits the target has the potential to do more damage than a bullet carrying less energy.

Energy, after all, is what powers such important functions as penetration, bullet expansion and tissue destruction.

But energy is an estimate of killing power only when comparing two similar calibers and bullets.

Compare a 200-grain bullet fired from a .35 Remington rifle to the same bullet fired from a .350 Remington Magnum and you’ll find that the magnum’s bullet carries more energy to the target and has been proven to have more killing power.

By the same token, compare a 130-grain .270 Remington Core-Lokt bullet with a 150-grain Core-Lokt in .30-06. You’ll find the .270 carries about 2,225 foot-pounds of energy at 100 yards, and the .30-06 about 2,281.

The two bullets are similar in performance and energy and are essentially identical in killing power. Decades of use on big game have proven this.

Energy figures can be misleading if dissimilar calibers and bullets are compared. Again using Remington Core-Lokts as a common denominator, a .30-30 at 150 grains carries less than 1,300 foot-pounds of energy at 100 yards. A .22-250 load of identical construction at 55 grains carries only about 40 fewer foot-pounds at the same distance.

Certainly the .22-250 and .30-30 are not equal as deer rounds. While the energy figures are comparable, the sectional density, frontal area, penetration, bullet performance (and consequently the killing power) are completely different.

We’re talking apples and oranges in this scenario. Granted, they are both fruit, but that’s where the similarity ends.

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This article was published in the Winter 2010 edition of Buckmasters Whitetail Magazine. Subscribe today to have Buckmasters delivered to your home.

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