Taylor KO Factor

The Taylor KO factor or TKOF is a formulaic mathematical approach for evaluating the stopping power of hunting cartridges developed by John "Pondoro" Taylor in the middle of the 20th century. Taylor, an elephant hunter and author who wrote two books about rifles and cartridges for African hunting, devised the formula as a means of comparing the ability of a cartridge to deliver a knock out blow to elephant from a shot to the head when the brain is missed.

Formula

The Taylor KO factor multiplies bullet weight (measured in grains) by muzzle velocity (measured in feet per second) by bullet diameter (measured in inches) and then divides the product by 7,000, converting the value from grains to pounds and giving a numerical value from 0 to ~150 for normal hunting cartridges. Expressed as a fraction, the Taylor KO Factor is:[1][2][3][4]

Example calculation

Using the standard 7.62×51mm NATO cartridge, the cartridge's characteristics are:

  • Bullet mass = 9.5 grams 147 grains
  • Muzzle velocity = 833 meters per second 2733 feet per second
  • Bullet diameter = 7.82 millimetres .308 inches

The calculation is:

Therefore the Taylor KO factor for the 7.62x51mm NATO cartridge is 17.9.

History

John "Pondoro" Taylor, an ivory hunter who over his career shot over 1,000 elephants along with a variety of other African game and who is renowned for writing two books about rifles and cartridges for African hunting, devised the Taylor KO factor to place a mathematical value on the concussive effects a cartridge and bullet would have on an elephant, specifically from a shot to the head when the brain is missed, a "knock out" meaning the elephant was sufficiently stunned by the hit that it would not immediately turn on the hunter or flee.[2][4][5][6][7][8]

First describing the Taylor KO Factor as "knock out value" or "strike energy" in his African rifles and cartridges, Taylor wrote that muzzle energy is "surely the most misleading thing in the world", that it is too dependent on muzzle velocity instead of bullet weight and that it is "quite useless if you are trying to compare any two rifles from the point of view of the actual punch inflicted by the bullet" which according to him is more affected by the bullet's weight. In African rifles and cartridges Taylor compares the effect of a near miss of an elephant's brain from a frontal head shot with the .416 Rigby and the .470 Nitro Express, two cartridges with similar muzzle energy but different bullet weights. Taylor states that the .416 Rigby will probably not knock the elephant out, but momentarily stun the animal which will recover quickly if not dispatched immediately, while the same shot delivered by the .470 Nitro Express will render the elephant unconscious for up to five minutes. Further, Taylor writes that the .577 Nitro Express will knock an elephant unconscious for around 20 minutes, the .600 Nitro Express around half an hour.[4][6]

The Taylor KO factor conforms to the observations and experiences of Taylor who, along with other very successful elephant hunters such as Deaf Banks, Pete Pearson and Jim Sutherland, preferred large heavy bore rifles for elephant hunting in close country.[2][4][9]

Criticism

Whilst most acknowledge the originality of the formula and Taylor's broad big-game hunting experience with a wide variety of cartridges, the Taylor KO factor is source of some debate amongst modern gun writers, some describing it as peculiar, antiquated, inaccurate and an unfounded theory, others stating it is a useful tool but stressing that should not be used in isolation when choosing a big-game hunting cartridge, whilst others still say their experiences tend to support the formula.[1][2][10][11][12]

Specific criticisms of the Taylor KO Factor include the emphasis placed on bullet diameter over factors such as sectional density and bullet expansion and the formula’s failure to account for modern bullet design. These factors, along with Taylor’s dismissal of muzzle energy, allow many obsolete low powered large bore cartridges such as the .577/450 Martini-Henry and the .45-70 Government to have as much as twice the TKOF than the smaller bore general purpose hunting cartridges such as the .303 British and the .30-06 Springfield. For these reasons the Taylor KO factor is seen as poor measure of stopping power for cartridges used on deer sized game and smaller, it is also seen as a poor measure of the performance of handgun cartridges.[1][2][3][13]

Taylor himself acknowledged this, stating "in the case of soft-skinned non-dangerous game, such as is generally shot at medium to long ranges, theoretical mathematical energy may possibly prove a more reliable guide" and that his formula was designed to measure a cartridge's performance against the large, thick skinned, big boned elephant.[4]

TKOF comparison

Below is a table including a number of African dangerous game hunting cartridges including their bullet mass, muzzle velocity, bullet diameter and Taylor KO factor, discussed in African rifles and cartridges.[4]

TKOFNameMass (gr)Velocity (fps)Diameter (in)
1.5.22 Long Rifle401200.223
5.65.56x45mm NATO † ‡622830.224
17.97.62x51mm NATO † ‡1472733.308
28.3.318 Westley Richards2502400.330
31.4.333 Jeffery3002200.333
30.4.338 Winchester Magnum2252800.338
30.2.350 Rigby2252625.358
34.6.375 H&H Magnum2352750.375
38.8.375 H&H Magnum3002400.375
49.2.400 Jeffery Nitro Express4002100.410
49.8.450/400 Nitro Express4002150.405
51.4.404 Jeffery4002125.423
57.1.416 Rigby4002400.416
59.9.425 Westley Richards4102350.435
67.5.450 Nitro Express4802150.458
69.3.450 No 2 Nitro Express4802175.458
74.7.450 Rigby4802378.458
70.3.458 Winchester Magnum5002150.458
76.2.465 H&H Magnum4802375.468
69.500/465 Nitro Express4802150.468
72.9.470 Nitro Express5002150.475
89.3.500 Nitro Express5702150.510
90.9.505 Gibbs6002100.505
128.3.577 Nitro Express7502050.584
147.5.600 Nitro Express9001850.620
200.700 Nitro Express10002000.700

Included as a comparison
Developed after Taylor's writings

References

  1. Steven Bowers, "The best all-round large bore rifle cartridge", African Expedition Magazine, vol 1 issue 2, Safari Media Africa, September 2008.
  2. Chuck Hawks, "The Taylor Knock-Out Factor", chuckhawks.com, retrieved 10 April 2018.
  3. Philip P. Massaro, Big book of balistics, Gun Digest Books, Iola, 2017, ISBN 978-1-4402-4711-8.
  4. John Taylor, African rifles and cartridges, Gun Room, London, 1948.
  5. Jim Carmichel, "Knockdown power: Here's why some calibers always seem to flatten game", outdoorlife.com, retrieved 1 June 2018.
  6. John Taylor, Big game and big game rifles, Herbert Jenkins, London, 1948.
  7. Brad Fitzpatrick, "Knockout punch", RifleShooter Magazine’s guide to big-game hunting, Skyhorse Publishing, New York, 2017, ISBN 978-1-5107-2076-3.
  8. Terry Weiland, Dangerous game rifles, 2nd ed, A Shooting Sportsman Book, 2009, ISBN 978-0-89272-807-7.
  9. James H. Sutherland, The adventures of an elephant hunter, Macmillan, London, 1912.
  10. Finn Aagaard, "Stopping power", huntforever.org, retrieved 4 June 2018.
  11. John McAdams, "Pros and cons of using the Taylor Knock-Out Factor", exclusive.multibriefs.com, retrieved 5 May 2018.
  12. Randy Wakeman, "Energy transfer and other bullet bullistics", randywakeman.com, retrieved 5 June 2018.
  13. Patrick Sweeny, Choosing handgun ammo: the facts that matter most for self-defense, Gun Digest Books, Zephyr Cove NV, 2017, ISBN 978-1-946267-03-0.
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