Saturday, December 22, 2012

Measuring Effectiveness of Cartridges: Thorniley Stopping Power

In our last post, we looked at a formula called the Taylor Knock Out Factor, which was developed by a big-game hunter with extensive experience with African wildlife. In this post, we will look at another empirical formula which was developed by another hunter, this one had extensive experience with wildlife in both Africa and North America. His name is Peter Thorniley and he developed the Thorniley Stopping Power Formula.

The Thorniley Stopping Power Formula is similar to the Taylor KO Factor we studied in the previous page. It is calculated as:
TSP = 2.866 * v * (m/7000) * sqrt(d)
TSP = Thorniley Stopping Power
v = velocity of the bullet in feet per second
m = mass of the bullet in grains
sqrt = square-root function
d = diameter of the bullet in inches.

Since this formula uses the square-root of the bullet's diameter (unlike the Taylor KO factor formula, which uses the bullet's diameter without taking the square root), the values are on a different scale than the Taylor KO factor numbers. Like the Taylor KO factor, the values obtained by the TSP formula are empirical.

The Thorniley scale is as follows:
Thorniley Stopping Power Suitable For
45 Antelope
50 White-tail Deer, Mule Deer etc.
100 Black Bear 
120 Elk, Moose, Kudu, Zebra etc.
150 Lion, Leopard, Grizzly Bear, Brown Bear
250 Hippopotamus, Rhinoceros, Cape Buffalo, Elephant
The values in the table above are based upon Peter Thorniley's long experience as a hunter.

Let's say that we have a .30-06 rifle (such as the M1903 Springfield rifle or the M1 Garand rifle). Let us assume that this rifle fires a bullet weighing about 180 grains and .308 inch diameter moving at around 2900 feet/sec. Plugging the numbers into the formula above, we have:
TSP = 2.866 * 2900 * (180/7000) * sqrt(0.308) = 118.61 approximately.

Looking up the TSP value on the table above, we see that a .30-06 rifle can be used to hunt antelopes, deer, black bears, elk, moose, kudus, zebras etc. (since 118.61 is pretty close to 120), but probably not such a good idea against lions, grizzly bears, hippopotamuses, rhinoceroses, elephants etc.


  1. I strenuously object to the description of the TKO or the TSP as "empirical". They were not arrived at by experimentation or observation, they were designed purely to weight various factors in order to get the results their creators wanted. The formals simply exist to give a false air of scientific rigor.

  2. I have to agree with Alex. If one uses the TKO or TSP formulas to compute something like a glacier, they would find it would score unimaginably high, whereas standing in front of a glacier won't do anything but perhaps make you a bit cold.

  3. Good point gentlemen. You are right that these formulae were invented by their creators to produce results based on their creators experiences. Thank you very much for the feedback :).