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Friends, please understand that this is a very complex subject, with many known and unknown variables that cannot be addressed or defined completely in an essay. Even if we wrote a book on this subject, we could not cover it completely. Please do not find fault with the fact that this essay could be 500+ pages long, but isn’t. This essay is an attempt to bring awareness to our customers, not to be 100% conclusive on the subject.

Many decades ago, some gun writers started comparing cartridge effectiveness by measuring and applying the cartridges ft-lbs (Kinetic) of energy. That trend of using ft-lbs to calculate “killing power” has become pervasive, industry wide. Kinetic energy may be a useful tool for measuring some things, which we will discuss, but today, ft-lbs of energy calculations are being applied in ways that are very misleading or not accurately applicable.

 First, let’s take a look at the mathematical calculation for bullet kinetic energy or ft-lbs of energy.  Kinetic energy of any given bullet is calculated in the following manner:


Let’s look at kinetic energy calculations for a typical 30-06 load of a 180gr. bullet moving 2,700 fps:


So what’s the problem????

The “problems” are several and meaningful!

1.  First, this formula uses velocity squared, so it will always give higher values to lighter, faster bullets and lighter, faster bullets are meaningless to an 800 lb. bull elk or more especially to a 2,000 lb. stomping mad Cape buffalo.
2.  Second, this calculation ignores bullet diameter, which is very important as the quarry gets bigger and tougher.
3.  Third this calculation ignores bullet shape..i.e. in general terms; a round nosed solid/non-expanding bullet will do less terminal damage than a flat nosed solid bullet.
4.  Fourth, it ignores bullet construction.

 As one example of the flawed ft-lbs formula, let’s look at one very early and popular good old standby 45-70 load compared to a modern 22-250 load.

The early 45-70 gained much of its big game killing fame by pushing a 405gr. lead round nosed bullet @ 1,350 fps with black powder….this load generates 1,638 ft-lbs of energy……The typical 22-250 load of a 50gr. bullet moving @ 3,850 fps generates a slightly higher number of 1,645 ft-lbs, but let me ask, which load would you want to hunt grizzly with?…..or better, which load would you want to try and stop a charging grizzly with?

 Let’s come back to the discussion of the usefulness of kinetic energy numbers after we discuss the TKO mathematic formula.

 TKO - Taylor Knock Out

TKO stands for Taylor Knock Out. John Taylor was a mid-20th century African hunter and poacher. Nobody knows how many thousands head of African game he killed, but it was several. His original KO formula was derived by observing how effective certain cartridges were in knocking out an elephant if it was shot in the head, but the brain was missed.

Taylor’s mathematical formula is thus.  Bullet diameter X weight in grains X velocity / 7,000 (7,000 grs. in one lb.)

Bullet Diameter X Bullet Weight X Velocity
7,000 (7,000 grains = 1 lb)

Taylors KO formula still does not factor the bullet shape, but assumes solid, non-expanding construction and does include the very important bullet diameter and further, it does not square the velocity, but gives velocity the single value it deserves. TKO numbers only have relevance if they are being compared to other TKO numbers…..comparing TKO numbers to ft-lbs would have no meaning.

The same above 30-06 load that we calculated would have 2,913 ft-lbs of energy for would give a TKO # of 21.39


Let’s compare the same 45-70 and 22-250 loads that we used in the above ft-lbs comparison……

45-70 Load



22-250 Load


See what happens when you include bullet diameter and do not square velocity? The old weak black powder 45-70 load generates a rating of 5X what the 22-250 load generates, for effectiveness on big game.

Is the TKO rating perfect for generating a number that will predict effectiveness on big game? No, absolutely not! No mathematic formula could be. However, the TKO formula will generate a number that I believe is far more meaningful on big game, than ft-lbs of energy.


So, where/when are kinetic energy numbers meaningful when applied to killing mammals? I believe that with super thin skinned, lightly constructed animals that weigh under 200 lbs., kinetic energy has a meaningful application, but remember that those kinetic energy numbers are still coupled with other factors that we cannot give a value to, such as bullet construction (mushrooming, fragmentation, secondary projectiles such as bone fragments, state of mind of the mammal being shot, etc., etc., etc.) and depth of penetration, etc. Thin skinned smaller animals like whitetail deer, humans, coyotes, etc. are all susceptible to the effect of faster lighter bullets. These types of animals do not require super deep penetration to be killed, so kinetic energy numbers have meaningful application, but not so with buffalo, grizzly, moose, etc. From a great deal of personal experience, I can tell you that the above 22-250 load would literally explode a 4 lb. Rock Chuck hit within normal shooting distances, but the old 45-70 load would just make a big hole in a Rock Chuck…… the Kinetic energy calculation is more meaningful with the small mammals, than with giant mammals.

This would be a good place to refer you to a couple other short essays that deal with related issues of bullet effectiveness on big game. Bullet jacket/core separation & Understanding “bonded” bullets-dispelling the myth.


Often, we over-think a topic and never come to a useful resolution, so let’s find the lowest common denominator in this discussion…..for me that means when we are killing big game, we need a hole that goes deeply enough to destroy organs and possibly frame supporting bones. The bigger this hole, the more effective it will be. Some types of big game only need 20 inches or so of penetration depending on body mass and angle of impact. Other types of big game need 6+ feet of penetration for the shot presented. Kinetic energy is almost (not totally) meaningless in this equation…….The TKO # will have much more meaning.

Choose your cartridge and your ammunition for that cartridge accordingly. Obviously it will require some kinetic energy to get that bullet down field and to penetrate the target sufficiently, but bullet size and design is a bigger part of that formula, than kinetic energy alone, when dealing with large animals.

Hopefully this essay will be useful to those of you who have been drinking the industry cool aid about kinetic energy that is sooooo continually repeated within this industry. This essay is only meant as an aid (not cool aid) to our customers and to the industry in general, in understanding some of the specifics that we seem to misunderstand regarding effectiveness of ammunition on living mammals.

Good shooting and God bless,