Taylor KO Factor

Taylor KO Factor is a commonly used mathematical approach for evaluating the stopping power of 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.

$\mathrm{TKOF}=\frac{m_{\mathrm{bullet}}\cdot v_{\mathrm{bullet}}\cdot d_{\mathrm{bullet}}}{7000}$ (Equation 1)

Where

$m_{Bullet}$ is the bullet mass in grains (1 pound = 7000 grains)
$v_{Bullet}$ is the bullet velocity in feet per second
$d_{Bullet}$ is the bullet diameter in inches

If the international standard units of grams, millimeters, and meters per second are substituted, the divisor can be changed from 7000 to 3500 to give approximately the same resulting TKOF.

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 or scientific basis and is strictly used as a figure of merit for comparing cartridges. Its main advantage is the ability to attempt to represent complex terminal ballistics as a number. This can be utilized to assign different wounding capabilities to projectiles in video games.

1 Background
- 1.1 Example Calculation
- 1.2 Alternative Approaches
2 References
3 Further reading
4 See also

Background

Example Calculation

Consider the case of a standard NATO 7.62 × 51 mm cartridge. It has the following characteristics:

diameter: 7.62 mm $\Rightarrow$ 0.30 inches
mass: 9.7 grams $\Rightarrow$ 150 grain bullet
velocity: 860 meters per second $\Rightarrow$ 2820 feet per second

The calculation is performed as shown in Equation 2.

$\mathrm{TKOF}=\frac{0.30 \cdot 150 \cdot 2820}{7000}=18.1$ (Equation 2)

Alternative Approaches

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:

kinetic energy
momentum
TKOF
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

None of these methods truly consider bullet construction, with the exception of TKO, which dealt mainly with solid bullets. An expanding bullet, for example, may have better "stopping" power over another design, due to the it's increased wound channel as the jacket opens, even though it may be traveling at a lower velocity. Just as a large diameter solid, at low velocity may have better "stopping" power, due to its deep penetration, than a small diameter hollowpoint at max velocity.

Bullet shape does not factor in these methods either. Example: A solid, wide flat nosed bullet, may create more impact damage, than a solid, pointed or round nosed bullet of the same caliber at the same velocity.

These variables combine to effect bullet penetration, and tissue damage, in different ways. Thus making a simple, single method of bullet effectiveness, difficult to quantify.

Some examples of TKO factor's, and the factory loaded cartridge's derived from, are as follows:

TKO Factor	Name	Mass	Velocity
70.33	.458 Win Mag	500gr	2150fps
42.86	.500 S&W	500gr	1200fps
36.48	.45-70	450gr	1250fps
37.71	.500 Linebaugh	440gr	1200fps
35.15	.475 Linebaugh	370gr	1400fps
29.77	.480 Ruger	325gr	1350fps
40.98	.375 H&H	300gr	2550fps
34.71	.405 Win	300gr	2000fps
30.22	.454 Casull	260gr	1800fps
22.84	.38-55	255gr	1650fps
19.86	.44 Mag	240gr	1350fps
12.30	.45 ACP	230gr	830fps
21.06	.35 Rem	200gr	2100fps
20.76	30-06	170gr	2850fps
10.44	.40 S&W	165gr	1080fps
11.28	.357 Mag	158gr	1400fps
14.85	.30-30	150gr	2250fps
7.31	9mm	115gr	1250fps
8.70	.243	85gr	2950fps
2.83	.32acp	71gr	900fps
5.78	.223	55gr	3300fps
1.33	.25acp	50gr	750fps
1.33	.22LR	30gr	1400fps

References

Taylor, John (1948). African Rifles and Cartridges. Highland Park, NJ: The Gun Room Press. ISBN 0-88227-013-3.
Porter, Greg (1989). Guns, Guns, Guns: Gun Design for Any RPG. New York, NY: Blacksburg Tactical Research Center. ISBN 0-943891-04-3.

Taylor KO Factor

Contents

Background

Example Calculation

Alternative Approaches

References

Further reading

See also