Kinetic energy is a good number if you're going to pick just one number to describe a bullet's terminal potential but it still falls short of capturing all of the relevant data needed to really make a good determination of terminal performance.
I think KE was picked because it was easier to sell new cartridges of a greater velocity because KE increased by the square the velocity, which makes a small velocity increase appear to be a huge improvement over a slower bullet of the same diameter. Momentum (ME) is conserved in a collision, KE is not, and Momentum being mass times velocity, it is a lot harder to increase momentum by a significant amount, without the shooter getting beat to heck.
Advertising in print magazines, has been worked, messaged, and evolved , since the American Civil War. The shooting community is not merely been shaped, but has been molded by the pseudo science put out by the Industry marketing departments who sponsor the articles we read. The idea that KE is a lethality measure, that you can calculate "stopping power", is one of the things that the shooting community has been taught to believe.
I believe that KE (and ME) are easy to calculate, therefore, easy to sell as a lethality measure. KE is more of a marketing number and gunwriters use the thing all the time to hype cartridges. All the cartridges we use are more or less bounded by the weight of the firearm, lets say a rifle. Ever carried a 12 lb or 15 lb rifle 1000 yards to the Viale pitts at Camp Perry? It ate up my shoulder. My target rifles have lots of lead weight in them, to cut the recoil, and I cannot imagine carrying them all day. The heaviest service rifles were around 8 to 9 pounds. I know Roy Dunlap claimed he almost died carrying a M1917 in basic. Also, the recoil momentum of 12 to 14 foot pounds used to be the estimated recoil limit for a Soldier. Now, with women in the service, the 223 cartridge is the max, with about 2 or 3 pounds
http://www.chuckhawks.com/recoil_table.htm. I wonder what Sargent York would have said. Now, I have fired some 40 foot pound 45/70 loads and have fired two 458 Win Mag loads, which are around 62 foot pound, and I don't want any of the 62 foot pound recoil in a 9 pound rifle. It hurt! Shoot enough forty foot pound recoiling cartridges, and you will feel "
like a duck stunned on the head". I have no idea what will happen to a person who shoots 50 plus full power 458 Win Magnum loads. Will they develop CTE?
Therefore, firearms corporations have a very difficult time developing a new round around an increase in momentum. Shooters would get knocked silly. But, if you sell KE as a quality and lethality measure, there is a lot more room for playing around before the shooter develops concussion from the recoil.
Martin Fackler
https://en.wikipedia.org/wiki/Martin_Fackler and other lethality testers came to the conclusion that KE was not a measure of lethality. You can read Fackler's papers, he nicely dismisses the knock down theories of in print gunwriters, saying in one article, they are nothing but advertising. If you read enough in print articles, especially from the past, you can tell they are physically incoherent. A simplified Fackler statement would be, if it lives and breathes, if you make it bleed enough, it will stop breathing. Fackler's papers are very positive about big through holes. But casting ballistic gelatin is work, and measuring the volume of the hole, and the depth of the hole, that is work. So, what we will continue to read in the popular press, is KE. Easy to calculate. Anyone remember the tables where a certain amount of KE was required to kill certain animals? Anyone remember the rules of thumb that a certain amount of KE was required to kill a deer, but more KE was required for a Moose? That was psuedo science.
Something else, where is the research into lethality that Industry funded? I don't think Industry funds research, and they don't need to. All they have to do is commission some in print gunwriter to write an article, (about $400) give the guy some psuedo science talking points, and they make profits. What I have noticed, was that the real lethality research was funded by the Navy. Martin Fackler was a Navy Doctor. Gun writers are guys who get $400 for an article, they go out into the garage, or the Hardware Store, buy what is available, and what I have read for decades, is that deer (or humans), are "like" wet newspaper, clay, wood, wood dowels, phone books, duxseal, milk jugs full of water, etc, etc. In print gunwriters have never really run calibrated tests against everything. Their calibration point is that they shot an animal, and the bullet performed similar to bullets shot in whatever was in their garage, or on the shelf of a hardware store. I just remembered, they used to compare divots in steel plates. People, animals, are like steel plates.
Knock down power, read enough accounts of Soldiers in combat, guys who had to be told, they were missing their feet. Knock down power is one of those created for advertising terms. Knock down power from small arms is the person's or animal's reaction to pain if the central nervous system is not turned off. You know, Hornets have incredible knock down power: get bite by one. You will jump and kick like a jackass. You will run as fast as you can, and flap your arms like a bird, trying to get away. You might roll around on the ground. Did anyone measure the KE of a Hornet sting?
When penetration on large game is needed, I'd go with the Taylor formula of heavier and better SD to ensure adequate performance where the lighter bullet might fail. With careful shot placement the smaller calibers can absolutely work just fine....but the stress on the projectile is magnified and many will fail. The very latest solid copper bullets seem to violate the conventional wisdom and can hold together while penetrating deeply so perhaps the playing field has been altered a bit. As always...the definitive answer remains....'It Depends'.
