What Is The Taylor KO Factor?

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What Is The Taylor KO Factor?

Keep reading to learn all about the Taylor KO Factor.

Developed by the legendary ivory hunter/poacher John “Pondoro” Taylor in the mid-1900s, the Taylor KO (Knock Out) Factor is one of many methods used for comparing the relative stopping power of big game hunting cartridges. While not perfect by any stretch of the imagination, the Taylor KO Factor is still an interesting and sometimes useful formula. Below is a full description of the Taylor KO Factor as well as an evaluation of its advantages and disadvantages.



What is the Taylor KO Factor?

The Taylor KO factor was developed by John Taylor as a way to compare the effectiveness of different big game hunting cartridges on large, thick skinned game. He formally introduced the Taylor KO Factor to the world in 1948 when he published his book African Rifles & Cartridges, though he probably developed the equation many years prior to the book’s publication.

The formula used to determine the Taylor KO Factor for a particular load is quite straightforward: simply multiply the mass of the bullet (in grains) by the velocity of the bullet (in feet per second) and its diameter (in inches). Then divide the result by 7000. The resulting number is the Taylor KO Factor for that particular load and has no unit of measurement (kg⋅m/s2, fps, ft·lbf, etc).

Using this formula, below are the Taylor KO Factors for several big game hunting loads.

.30-06 Springfield (180gr Nosler Partition at 2,750fps): 21.8

.375 H&H (300gr Hornady DGX at 2,530fps): 40.7

.378 Weatherby Magnum (300gr FMJ at 2,925fps): 47.0

.458 Winchester (500gr Hornady DGX at 2,140fps): 70.0

.600 Nitro Express (900gr Kynoch solid at 2,000fps): 159.4

Though we’ll never know precisely what was going through his head at the time, it certainly appears that John Taylor devised the Taylor KO Factor to conform to his personal experiences and views when it came to choosing the ideal bullet for big game hunting. He was known for being a strong proponent of large bore rifles shooting heavy bullets at a slow to moderate velocity when hunting big game, especially elephants. Especially when compared to the kinetic energy formula (E= ½mv2), the Taylor KO Factor formula is strongly weighted towards heavy, large diameter bullets.

This is likely because Taylor wanted a round that would stun or even knock out a large dangerous game animal (like a buffalo or an elephant) with a shot to the head, even if it missed the brain. Especially with the bullets available to him, using heavy, large bore bullets was the best way to accomplish this. At the time, and under less than ideal situations, lightweight, high velocity bullets were much less likely to work, hence the weighting of the formula towards heavy bullets at moderate velocity.

For instance, the .378 Weatherby Magnum load in the chart above actually has more muzzle energy than the .458 Winchester Magnum (5,699 ft·lbf vs 5,084 ft·lbf). However, the .458 Winchester has a Taylor KO Factor nearly 50% larger than the .378 Weatherby because that load fires a bullet that is significantly heavier and has a larger diameter, which more than offsets the significant velocity advantage of the .378 Weatherby.

Advantages of The Taylor KO Factor

The Taylor KO Factor provides several advantages to a hunter looking to select an appropriate load for big game hunting. For one thing, the formula is extremely easy to use. The Taylor KO Factor formula is designed to be used with the typical units of measurement that most American hunters are used to working with: mass of the bullet in grains, velocity of the bullet in feet per second, and diameter of the bullet in inches. Furthermore, calculations are very straightforward and can be quickly performed on a basic calculator or even by hand.

Additionally, the Taylor KO Factor provides a very simple and easy to understand comparison between various different big game hunting cartridges. For instance, looking at the chart above, it is obvious that the .458 Winchester has a larger Taylor KO Factor than the .375 H&H, which in turn has a larger Taylor KO Factor than the .30-06 Springfield. These numbers pass the “eyeball test” and generally conform to the reality concerning the relative stopping power of the three cartridges.

Disadvantages of the Taylor KO Factor

Unfortunately, there are some major issues with the Taylor KO Factor. First off, the formula seems to be devised to fit personal experiences. Even though John Taylor was one of the foremost experts of his time when it came to hunting big game, the fact that this equation was devised to fit his preconceived notions, rather than as a result of any scientific testing, should be enough to make you want to take the results it generates with a grain of salt.

Additionally, the Taylor KO Factor is a product of the time that John Taylor lived in and the equipment he had access to. At the time, there were no “controlled expansion” bullets to speak of (the Nosler Partition was not commercially available until 1948) and a big game hunter had a choice between solids and poor quality (by modern standards) expanding bullets. Because there was such a high likelihood of experiencing some sort of failure when using many of the bullets available at the time, John Taylor and his contemporaries tended to favor larger bore rifles, which were more likely to successfully kill or cripple the targeted animal even if they experienced a bullet failure.

However, over the past few decades, there have been numerous advances in bullet design and construction. Modern expanding bullets will both expand more reliably and penetrate deeper than the bullets Taylor had access to. At the same time, modern solids will also generally penetrate deeper and are less likely to deform or deflect when compared to the bullets used in the early 1900s. Because modern hunters have access to much higher quality bullets, it is possible to safely and ethically use many cartridges and loads that have a relatively low Taylor KO Factor when hunting big game.

While the Taylor KO Factor certainly provides some interesting information, I would not bet my life solely on a hunting load based solely on its Taylor KO Factor. There is nothing wrong with using it, along with several other factors, such as sectional density, momentum, and kinetic energy, to make an informed decision when choosing a cartridge and load for big game hunting. However, there are many more factors involved in the stopping power of a load and relying solely upon the Taylor KO Factor will give you an incomplete picture of the true potential of your hunting load.

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The book African Rifles and Cartridges by John Taylor and the web site Chuck Hawks were used as sources for this article.


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