Debunking the Infamous Rifle Knockdown Power Myth

For generations, gun writers have endlessly discussed knockdown power, a topic that never seems to lose its appeal among readers.

Personally, I have refrained from contributing to this topic not because I lack opinions, but because I have too many. However, recent research has brought forth documented evidence, based on scientific studies, that sheds light on why some calibers exhibit exceptional “knockdown power” while others do not. The unexpected answer to this debate is bound to fuel further discussions. But before we delve into the details, let’s first clarify what knockdown power means and how it is generally perceived.

First and foremost, the term “knockdown power” is misleading. Unless we are talking about a giant cannonball or a car colliding with a deer on a dark highway, knockdown power, in the context of sporting-rifle bullets, refers to an animal’s physical reaction upon being hit by a bullet. Specifically, if an animal falls immediately as if its earth beneath it has been snatched away, it is said to have been knocked down, and the hunter, wise in his cartridge choice, congratulates himself. Conversely, if the animal does not fall immediately and continues to wander or dash away even after being hit, the cartridge or bullet may be deemed weak, and the manufacturer may face criticism.

However, the truth of the matter is that no big-game caliber is consistently good or bad, and therein lies the complexity of the issue.

The Lights-Out Method

In the past, when still hunting was popular and shots were taken at close range, whitetail deer hunters often aimed for the head or neck. This method, also known as the “lights-out” method, could effectively achieve near-complete knockdown effect by targeting the brain or shattering the neck vertebrae and spinal cord. These were the preferred shots by seasoned deer hunters as they helped preserve meat and usually brought the animal down on the spot.

However, hunting techniques and equipment have evolved, making neck or brain shots less common. Aiming at smaller parts of an animal’s anatomical structure is a hit-or-miss endeavor.

Taylor’s Theory

Another theory about knockdown power is centered around overwhelming the animal with bullet size, which can be referred to as the “bulldozer effect.” John Taylor, a seasoned gun enthusiast with extensive African experience, advocated for using big heavy bullets. He believed that bullet energy calculations disproportionately favored velocity, leading him to develop a system for calculating the Knock-Out Value of various calibers.

While there is merit to the idea that big calibers can have a significant impact on game, the effectiveness of this approach diminishes when considering the issue of declining marksmanship. Many hunters struggle with handling hard-kicking rifles and may flinch and jerk when firing, resulting in poor shot placement.

Weatherby’s Theory

On the other side of the debate are advocates who argue that high-velocity bullets, capable of transmitting shockwaves through the nervous system, are more likely to instantly incapacitate game animals. Roy Weatherby was a prominent advocate of this theory, emphasizing the importance of velocity. The term “hydrostatic shock” is often used to describe the circuit-breaking effect caused by high-velocity impact.

Combining the opposing elements of both theories and firing big, heavy bullets at high velocities may seem like a surefire way to maximize knockdown power. However, anyone who has fired a powerful magnum cartridge quickly realizes that this approach has its drawbacks.

Regardless of which theory one supports, there are countless examples of well-hit game with various calibers and cartridges that did not exhibit immediate knockdown. It is clear that the issue is more nuanced than a simple formula.

A Better Theory

A few years ago, while bird-watching in Namibia, I stumbled upon an article in a South African outdoor magazine that presented a fresh perspective on knockdown effect. Unlike the typical discussions about ballistics and penetration, this article offered insights from a controlled study conducted by professional veterinarians engaged in buffalo culling operations.

Unlike our opinions on knockdown power, which are often based on isolated incidents, this study collected data from multiple animals and subjected them to scientific examination by professionals. The researchers discovered that animals that were instantly knocked down exhibited massive blood vessel damage in their brains upon examination, while those that did not fall immediately showed no such damage. The conclusion drawn from this observation was that bullets that kill instantly often strike at the exact moment of the animal’s heartbeat, causing a sudden surge in blood pressure that leads to vessel ruptures.

This theory offers a plausible explanation for the knockdown phenomenon and provides answers to previously unanswered questions. However, it also introduces a new challenge: how to time a shot to coincide with the animal’s heartbeat.

Anecdotes from the Field

Many hunters form opinions on knockdown power based on limited field experiences. I have personally witnessed examples that defy expectations. Moose, known for their toughness, have been observed walking away after being hit. On one occasion, I planned to use this knowledge to my advantage when encountering a moose standing in freezing water. Armed with a .44 Magnum revolver, my plan was to shoot the moose, prompting it to move out of the water, and then finish it off with additional shots. However, my first shot brought the moose down faster than any previous caliber I had used.

Conversely, I have also encountered situations where animals were not immediately knocked down despite well-placed shots with powerful calibers. The issue becomes even more perplexing when considering the effect of adrenaline on an animal’s ability to be knocked down. Understanding terminal ballistics requires careful observation and consideration of various factors.

The Cape Buffalo Test

During an African hunt for giant eland, I found myself face to face with two Cape buffalo bulls. Normally, hunting such dangerous game requires a caliber like a .375 H&H or even a .458 Win. Mag. However, the only rifle I had was chambered in .338 Win. Mag. Nonetheless, I decided to take my chance and fired into the heart-lung area of one of the buffalo. To my amazement, the bull dropped immediately, showcasing an unprecedented demonstration of knockdown effect.

These experiences have led me to reconsider the notion of knockdown power and its underlying physiology. The heartbeat theory, although frequently observed by hunters, has only recently been understood. It serves as a valuable reminder that there is no infallible solution or magic cartridge capable of consistently bringing an animal down. Shot placement and bullet selection are critical factors in maximizing the potential for immediate incapacitation.

Understanding Terminal Ballistics

The true essence of killing power lies in breaking down vital organs responsible for supplying blood to the brain. Bullet mass, velocity, and kinetic energy do not act as meteoric forces that instantly flatten game. As many bowhunters can attest, even low-energy levels can be lethal, as demonstrated by numerous poached deer, elk, and moose killed with a .22 long rifle.

Contrary to popular belief, bullet energy alone cannot guarantee the desired knockdown effect, even if the bullet remains inside the animal and expends all its energy there. Countless instances have proven otherwise. What truly matters is bullet placement and the ability to maximize vital tissue destruction. Specialized bullets that fragment, expand, or create wide exit wounds can enhance the effectiveness of a shot. The selection of ammunition plays a critical role in achieving a swift and ethical kill.