You need enough energy to cause proper penetration of the bullet type used and enough energy to cause the bullet to perform as designed (fragment, expand/mushroom, etc.).
That has absolutely nothing to do with "hydrostatic shock, a pressure wave caused by the transfer of energy". The only place that has any validity is (possibly) with a shot to the liver (basically a loose/fragile bag of blood).
You are right though, I didn't cite any research. I apologize. Try the link below. That one should be all you need to start you on the road to enlightenment. If you are still curious when finished, do a search for some of the references at the end of it.
By the way, M.L. Fackler, M.D. is actually Colonel M.L. Fackler, M.D., the Director of the Letterman Army Institute of Research, Division of Military Trauma Research, Presidio of San Francisco.
He headed complete ballistics and forensic labs, had the doctors, physicists, and ballistics engineers to staff them, and the budget to fund the research. His teams spent many years studying not only human corpses (autopsies) and animal carcasses (necropsies) but ballistic gelatin and what nobody else had ever done, high speed x-rays of living animal flesh as bullets were damaging it. While their focus was military, they studied a wide variety of different types of projectiles from spherical to fragmenting to FMJ to VLD, etc.
In the paper below (only one of many) he also addresses some of the consequences of the common misconceptions about wound (terminal) ballistics, which has not only included poor weapons design parameters, but also (obviously) the State of Illinois' hunting regs.
http://rkba.org/research/fackler/wrong.html
Attempts to explain wound ballistics (the study of effects on the body produced by penetrating projectiles) have succeeded in mystifying it. Fallacious research by those with little grasp of the fundamentals has been perpetuated by editors, reviewers, and other investigators with no better grasp of the subject. This report explains the projectile-tissue interaction and presents data showing the location of tissue disrupted by various projectiles. These tissue disruption data are presented in the form of wound profiles. The major misconceptions perpetuated in the field are listed, analyzed, and their errors exposed using wound profiles and other known data. The more serious consequences of these misconceptions are discussed. Failure in adhering to the basic precepts of scientific method is the common denominator in all of the listed misconceptions....
MAJOR MISCONCEPTIONS
1. Idolatry of Velocity:...
2. Exaggeration of Temporary Cavity Size, Pressure, and Effect:....
3. Assumption of Bullet "Tumbling" in Flight:....
4. Presumption of "Kinetic Energy Deposit" to Be a Mechanism of Wounding:....
Many body tissues (muscle, skin, bowel wall, lung) are soft and flexible--the physical characteristics of a good shock absorber. Drop a raw egg onto a cement floor from a height of 2 m; then drop a rubber ball of the same mass from the same height. The kinetic energy exchange in both dropped objects was the same at the moment of impact. Compare the difference in effect; the egg breaks while the ball rebounds undamaged. Most living animal soft tissue has a consistency much closer to that of the rubber ball than to that of the brittle egg shell. This simple experiment demonstrates the fallacy in the common assumption that all kinetic energy "deposited" in the body does damage....