There is much discussion about stopping power. This is of concern by those permit carriers who are concerned with quick aggression negation and hunters striving for clean humane kills on game. Terminal ballistics is the study of the dynamics of the projectile and its interaction with the target. It is a wide field ranging from paper targets of the competitor to the destruction of thin-skinned vehicles by military marksman. But of particular interest is what happens inside the body of an aggressor or the how you can bring down that mule deer.
Bullet Kinetic Energy
The primary thrust is to transfer as much kinetic energy to the target a possible. This is a function of bullet weight, velocity and penetration. Penetration in turn is the function of the sectional density or mass in pounds divided by the square of the diameter of the bullet and is related to momentum or the mass times the velocity. Ethical hunting demands quick humane kills, while self-defense in turn strives for a quick neutralization of an aggressive, armed attacker(s). To accomplish these goals, it is necessary to severely interrupt or stop the flow of oxygenated blood to the brain by causing damage to the main blood bearing organs or causing significant damage to the vascular system. Second cause of damage is the disruption of the brain and central nervous system.
Bullet construction contributes significantly to the kind of wound cavity produced in soft tissue. The permanent cavity is the primary contributory factor in a quick incapacitation, desirable in a self-defensive situation and death when hunting. In self defense you are shooting not to kill but to stop dangerous aggressive behavior. In hunting the goal is a quick and effective kill.
Big Game Hunting
Tissue when hit by a projectile traveling at velocity behaves like a fluid. The bullet does not immediately penetrate the skin into the tissue but creates an ‘impact crater’ that stretches until failure and the projectile penetrates the tissue. The tissue is pushed ahead of the bullet violently until stretched beyond its elasticity and is cut and torn but quickly returns to its original position. As the bullet travels the wound channel opens like a stone hitting a pail of water at speed. It opens creating a temporary wound channel that is a major mechanism in disrupting nerve channels, tearing muscle and ripping arteries and veins.
Bullet Jacket & Meplat
The jacket plays a major role in the bullet’s terminal characteristics. Heavy, thick jackets tend to maintain their integrity holding the bullet together for deep penetration. Thick jackets on target bullet do not deform well even the hollow points. Lighter jackets tend to fragment and more easily expand, creating a wider wound channel and higher temporary cavitation, but don’t readily achieve deep penetration. Expansion is controlled through jacket design and bullet meplat, the very tip of the bullet. Soft points, polymer inserts and open hollow points that allow controlled expansion. But the bullet mustn’t give up all its kinetic energy until deep in the body to reach vital organs and the central nervous system. If the temporary cavity is not deep enough an aggressor may continue to be a danger and in game it prevents a quick kill, leading to suffering, crippling and a long hard death for the game animal. The higher the SD or sectional density it will affect this penetrative quotient as well. The higher the SD the longer the bullet will be for the caliber, generally speaking, the deeper a high SD bullet will penetrate for the striking velocity.
Bullet Velocity & Drag
Velocity is an important component. On long range shots the bullet must have enough velocity to penetrate deep to the vital organ area. It is around 230 ft/sec for human skin. Some low velocity defensive cartridges have failed to penetrate heavy winter clothing. The bullet as it expands increase its drag. The serves to make the tissue in front of the bullet denser as it cannot displace from the bullets path a quickly. For varmints the bullet has a relatively thin jacket and literally disintegrates on contact. Medium game and self-defense requires controlled energy release and deep penetration with good energy retention for transfer to internal organs. Dangerous game tends to use big, heavy, usually non-expanding bullets at moderate velocity to achieve deep penetration through tough thick hides, heavy muscles and large bone.