Taylor KO Factor
Taylor KO Factor is a commonly used mathematical approach for evaluating the
stopping powerof hunting cartridges. The term "KO" is an acronym for "Knock Out." The Taylor KO Factor (TKOF) is a figure of merit that allows hunters to compare bullets with respect to stopping power. The TKOF was developed by John "Pondoro" Taylor, a famous mid-20th century hunter and poacher of African big game. The factor is computed using Equation 1.
: (Equation 1)
* is the bullet mass in grains (1 pound = 7000 grains)
* is the bullet velocity in
feet per second
* is the bullet diameter in inches
Taylor first described this measure of stopping power in his classic work "African Rifles and Cartridges" (Reference 1). In this work, Taylor did not actually state Equation 1. In fact, he stated in Reference 1 that "I do not think there is any necessity to go into the methods I employed to arrive at the formula I used, suffice it to say that the final figures agree in an altogether remarkable way with the actual performance of the rifles under practical hunting conditions." However, it is obvious from the text and his presentation that he used Equation 1.
Taylor referred to number generated by Equation 1 as the "Knock Out Value" or "Strike Energy." Common practice today is to refer to this value as the "Taylor KO factor" or simply "Taylor KO."
In Equation 1, the denominator value of 7000 is a scaling factor. It can be viewed one of two ways:
* as converting the units of bullet mass from grains to pounds.
* giving the TKOF a convenient numerical value from 0 to ~150 for normal hunting cartridges.
The TKOF has no physical meaning and is strictly used as a figure of merit for comparing cartridges.
While pursuing his legendary hunting activities, Taylor observed that some cartridges were more effective at stopping elephants than others. He drew a clear distinction between stopping power and killing ability. Since he was always aiming for a brain shot, a properly placed shot with any of the cartridges he evaluated would kill an elephant. He was more concerned with the case where the shot missed the brain and the wounded elephant could turn and attack him. He wanted a cartridge that would "knock out" an elephant even when the bullet struck in a location that was not immediately lethal. To Taylor, a "knock out" simply meant that the elephant was sufficiently stunned by the hit that he would not immediately turn on the hunter. This would allow the hunter sufficient time for an accurate follow-up shot.
Discussions of numerical methods for evaluating cartridge effectiveness has a long history. Many of these methods were popular in the early to mid-20th century. There has been a recent surge in interest in stopping power formulae with the advent of video games. These games use these methods to evaluate the effectiveness of the weapons chosen by the game players. Reference 2 contains a list of the formulae in use by gamers.
Consider the case of a standard NATO 7.62 × 51 mm cartridge (also known as the .308 Winchester) . It has the following characteristics:
* diameter: 7.62 mm 0.308 inches
* mass: 9.7 grams 150 grain bullet
* velocity: 860 meters per second 2820
feet per secondThe calculation is performed as shown in Equation 2.
: (Equation 2)
Using numerical methods to evaluate the effectiveness of rifle cartridges has a long history and has been subject of much debate. The most common numerical methods used to evaluate the stopping power of cartridges are:
* Thorniley Stopping Power
Each figure of merit weighs the cartridge characteristics differently. Some methods are based on fundamental physics (e.g kinetic energy), while other methods are based on heuristic methods. Some of the more common figures of merit are:
* kinetic energy: favors high velocity, lower mass bullets (no diameter dependence)
* momentum: favors moderate velocity, moderate mass bullets (no diameter dependence)
* TKOF: favors large diameter, moderate velocity, heavy bullets
* Thorniley Stopping Power: favors moderate diameter, moderate velocity, moderate mass bullets
*cite book | first=John| last=Taylor| title=African Rifles and Cartridges | publisher=The Gun Room Press | location=Highland Park, NJ | year=1948 | id=ISBN 0-88227-013-3
*cite book | first=Greg| last=Porter| title=Guns, Guns, Guns: Gun Design for Any RPG | publisher= Blacksburg Tactical Research Center| location=New York, NY | year=1989 | id=ISBN 0-943891-04-3
*cite book | first=Peter| last=Capstick| title=A Man Called Lion| publisher=Safari Press | location=Huntington Beach, CA| year=1994 | id=ISBN 1-57157-011-X
*cite book | first=John| last=Taylor| title=Maneaters and Marauders | publisher=A.S. Barnes and Co| location=New York, NY | year=1948 | id=ISBN 1-57157-311-9
* [http://www.beartoothbullets.com/rescources/calculators/php/taylor.htm Taylor Knock-Out Factor Calculator]
* [http://www.beartoothbullets.com/rescources/calculators/php/thornily.htm Thorniley Stopping Power Calculator]
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