Models don't attempt to further fundamental science. They are very specific and, if done properly, use existing science to make useful computations for practical purposes. Whoever came up with the sectional density model did use basic physics. I'm certain that person did not set out to solve the general problem of bullet dynamics in arbitrary media.
There is nothing more to the sectional density model than what I explained it's based on.
The "Taylor Knock-Out Factor" is another model the gun community pushes. It is a model, but is wrong from a physics basis.
I am going to claim that Gunwriters have attempted and continue to attempt to make lethality a precise science. Sort of like that
dismal science, Economics. If you examine economic literature, the majority of what you read are mathematical models based on neo classic economics.
from Wiki:
If anyone did not notice, neo classicist mathematical models did not predict the Great Recession of 2008. Economists and gunwriters both have the same problem, they want to predict the future, given some simple inputs, and both camps have failed totally.
I remember when the Hatcher Index was dogma in the IPSC community. Hatcher created a simple model, based on momentum, added a shape factor for the bullet. The 45 ACP came out of to 20 on the revised Hatcher models, and is the baseline for determining what is a “major” round, lesser recoiling rounds are dismissed as "minor". Hatcher assumed that momentum was correlated to lethality, but he never conducted any tests to determine if his intuition was correct. (It was not)
The Kinetic energy school has been dominate among gunwriters primarily because it favors velocity. This is typical:
Weatherby promoted high velocity bullets, and according to Weatherby, you just have to hit the animal somewhere, anywhere, and that “wallop” does the rest. Gunwriters have created chapters of tables, ranked by kinetic energy, and animal type. It takes this much kinetic energy to kill this size of animal, more for this size. Of course, it is all nonsense and drivel, but it evolved from the problems gunwriters have on selling new rounds which are essentially identical to existing rounds. It is a lot easier to increase velocity, and hence KE than it is to increase momentum. Momentum is mass times velocity, but kinetic energy is mass time velocity squared. Squaring that velocity increases that fantasy chasm, that gunwriters need to push product, when shilling for the new, against the old.
If you notice, the market has sort of hit a wall on pressures. Cartridge pressures that run at 65,000 psia are the upper limit for reliability, and even then, temperamental at those pressures, causing all sorts of over pressure problems. Cartridges that regularly run at high pressures frequently have pressure issues because itty bitty changes cause pressures to spike, and the brass case materials just don’t have any margin at those pressures.
Also, Ackley Improved cartridge shapes have dominated the post WW2 market. A straight taper cylinder maximizes powder charge, but those shapes don’t feed well or extract well. Taper is good for feeding and extracting, but that taper takes away from case volume. Increasing case volume increases powder charges, which lead to a velocity increase. Increased velocity is what the market wants, or what the market has been taught to want, hence, what we see with these Ackley Improved type of cases, are detachable magazines, that precisely orient the top round, so the sucker will go in the chamber, but reduce magazine capacity from 5 rounds to three rounds. And if the magazine lips get a slight bend, the straight walled cartridge misfeeds.
After combustion, a taper cartridge will relax off the chamber walls at a diagonal, increasing clearance between case and chamber, but the straight walled case will come off at a straight line, and drag on extraction. Which increases the probabilities of stove pipe jams as the case falls off the bolt face. This is a particular problem with the 5.56, it is called “extractor lift”. The 5.56 is very straight walled, made according to the theories of Ackley, and it drags on extraction. You can see a presentation on this here:
https://ndia.dtic.mil/2003/smallarms/2003smallarms.html , it is under session VI, look for
Understanding Extractor Lift in the M16 Family of Weapons. What you see in the presentation, is that the 5.56 case drags under extraction, and to eliminate that drag, for the purpose of test, they had to grease the rounds. If anyone noticed, both the Soviet 7.62 X 39mm and the Chinese 5.8 mm round have a lot of taper and it is not by accident. The 7.62 X 39 feeds and extracts exceeding well with brass or steel case materials.
Shrinking bore diameter does flatten trajectory, but barrel life is awful. I met one Camp Perry competitor who was using a 22-250. His bullets shot flat, but his bore was toast in 1000 rounds. He said there was no rifling for about 12 inches in front of the chamber! Another, was using a 243 Win, and replaced his barrel every 800 rounds. Lets see, a $300 match grade barrel, $250 for the barreling job, and 800 rounds later, $600 dollars for a replacement. (including shipping and insurance) The 243 guy was his own gunsmith, most of the gunsmiths I have dealt with are buried with work. If you get your action rebarreled in under a year, you are lucky.
The current gunwriter theme is to push ballistic coefficient, as a quality attribute. We will see how that works out. I predict it will hit a physical wall.
Mass marketeers are ingenious, and will figure other ways to convince us to spend our money on their products. We are just putty in their hands.
and that is an accurate and light recoiling round. The Range Master at the 600 yard range at CMP Talladega was hitting golf balls at 600 yards, with his 6.5 CM, so, the round definitely has potential. I earned my Distinguished Rifleman's badge with a 308 Win M1a, so I will always have a soft spot in my heart for that round.
