Duncan MacPherson has already talked about the fallacy of using energy to evaluate/analyze terminal ballistic performance.
every now and then someone wants to analyze or think about a problem involving energy, and when they attempt to do this without really understanding energy or other thermodynamic concepts the result is unfortunate. One such problem is the analysis of any of the various aspects of terminal ballistics; some individuals with inadequate technical training and experience have unwisely and unproductively attempted to use energy concepts in the analysis of bullet impact and penetration in soft tissue. (Many others have simply assumed that energy is the dominant effect in Wound Trauma Incapacitation; this assumption is even more simplistic than the attempt to actually analyze the dynamics problem with energy relationships, and is no more successful).
Any attempt to derive the effect of bullet impact in tissue using energy relationships is ill advised and wrong because the problem cannot be analyzed that way and only someone without the requisite technical background would try. Many individuals who have not had technical training have nonetheless heard of Newton’s laws of motion, but most of them aren’t really familiar with these laws and would be surprised to learn Newton’s laws describe forces and momentum transfer, not energy relationships. The dynamic variable that is conserved in collisions is momentum; kinetic energy is not only not conserved in real collisions, but is transferred into thermal energy in a way that usually cannot be practically modeled. The energy in collisions can be traced, but usually only by solving the dynamics by other means and then determining the energy flow.
Duncan MacPherson from the book "Bullet Penetration"
When someone says use this bullet weight or that bullet weight because of summer or winter because of a winter coat - I think they're leaving out an important aspect of the decision making process, that being what can any particular round be expected to do using some valid predictive analysis.
It's not just about a bullet weight or velocity.
I can show you a 124gr +P hollow point that will penetrate 18" in the FBI Heavy Clothing test, and also penetrate 18" of ordnance gel after going through 4 layers of denim. I can also show you a 147gr +P round that will only penetrate 11"
Unless you believe in hydro-static shock or some as-yet-undefined characteristic of bullets that would stop assailants other than damaging vital tissue, you have to make some decision on what penetration is necesary to damage vital tissue.
You have to come to some conclusions about what you think is adequate penetration, what poses a risk of over-penetration for your situation.
Human bodies can be categorized with a bell curve. The average weight of an adult male in the United State is 189.8 lbs. The average shoulder width is somewhere around 17.5" The average male chest measurement is 40", the average waist is 34".
Do you just want to prepare for the 50th percentile? Do you want to be prepared for the 75th percentile? Do you want to be prepared for an individual who is at the extreme end of the spectrum for width and muscle mass ( probably no single shot from a 9mm pistol is going to ensure that you stop such an individual)
Once you have an idea of what you want a bullet to do, you have to look at each cartridge, and see what it actually does in gel tests.
It's a more complicated process than just getting the KE product out one end of an equation.
IMO you have to look at each cartridge, and see what it actually does in gel tests.