Developed by the legendary ivory hunter/poacher John "Pondoro" Taylor in the mid-1900s, the Taylor Knock-Out (or KO) 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 Knock-Out Factor is still an interesting and sometimes useful formula. Below is a full description of the Taylor Knock-Out Factor as well as an evaluation of its advantages and disadvantages.

What is the Taylor Knock-Out Factor?

The Taylor Knock-Out Factor was developed as a way to compare the effectiveness of different big-game hunting cartridges on large, thick-skinned game. Taylor formally introduced the Taylor Knock-Out Factor to the world in 1948 when he published his book "African Rifles and Cartridges," though he probably developed the equation many years prior to the book's publication.

The formula used to determine the Taylor Knock-Out 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 7,000. The resulting number is the Taylor Knock-Out 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 Knock-Out Factors for several big-game hunting loads.

  • .30-06 Springfield (180gr Nosler Partition at 2,750 fps): 21.8
  • .375 H&H (300gr Hornady DGX at 2,530 fps): 40.7
  • .378 Weatherby Magnum (300gr FMJ at 2,925 fps): 47.0
  • .458 Winchester (500gr Hornady DGX at 2,140 fps): 70.0
  • .600 Nitro Express (900gr Kynoch solid at 2,000 fps): 159.4

Though we'll never know precisely what was going through his head at the time, it certainly appears that Taylor devised the Taylor Knock-Out 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 Knock-Out Factor formula is strongly weighted toward 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. Using heavy, large-bore bullets was the best way to accomplish this with the bullets available to him. 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 toward 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 Knock-Out Factor nearly 50 percent 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 Knock-Out Factor

The Taylor Knock-Out 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 Knock-Out 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 straightforward and can be quickly performed on a basic calculator or even by hand.

Additionally, the Taylor Knock-Out Factor provides a simple comparison between various different big-game hunting cartridges. For instance, looking at the list above, it is obvious that the .458 Winchester has a larger Taylor Knock-Out Factor than the .375 H&H, which in turn has a larger Taylor Knock-Out 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 Knock-Out Factor

Unfortunately, there are some major issues with the Taylor Knock-Out Factor. First off, the formula seems to be devised to fit personal experiences. Even though 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 Knock-Out Factor is a product of the time in which Taylor lived and the equipment to which he had access. 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, 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, in 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 used. 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 Knock-Out Factor when hunting big game.

While the Taylor Knock-Out Factor certainly provides some interesting information, I would not bet my life on a hunting load based solely on its Taylor Knock-Out 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 Knock-Out Factor will give you an incomplete picture of the true potential of your hunting load.