What to Believe About Stopping Power
There has been some discussion on “stopping power” of late so I think it’s time that we get a few things straight. First off, “stopping power” or “knockdown power” doesn’t exist. Velocity exists. Foot pounds exist. Momentum exists. Even tissue disruption can be quantified but there is no magical force called “stopping.”
The term “stopping power” is, at best, an awkward attempt to quantify the ability of a given cartridge or load to incapacitate an attacker. It may surprise you to know that Cracky McCrackerson, your friendly neighborhood crack head/rapist/burglar actually has no idea that your grandpappy’s 1911 is supposed to take a man’s arm off when it whizzes past. He doesn’t know that the toothless suspender guy who seems nailed to that creaky stool at the gun store told you so. He doesn’t know that every gun rag ever written proclaims how singularly badass the .45 ACP is and how you have to buy a $3,000 1911 because ‘Merkah! You have to convince his body to stop trying to harm you. This is called “incapacitation.” What causes incapacitation, though?
Incapacitation is the result of physical trauma that substantively reduces a person’s ability to present a lethal threat. That trauma is either the result of damage to the central nervous system (CNS), or the result of hypovolemic shock (blood loss). CNS damage typically results in instant incapacitation and even a small amount of damage nearly anywhere in the brain or spinal cord can be effective. Hits to the upper spinal cord, brain stem, or cerebellum are most effective, though. Blood loss takes time and is dependent on which structures were damaged and to what degree. Good shot placement and a solid, three dimensional understanding of anatomy can help to ensure your bullets damage the right structures but what about the amount of damage done to them? Is a bigger bullet really better?
When a projectile passes through tissue, it pushes some tissue to the side and it tears or cuts through some tissue. The space lefty by tissue that is merely pushed aside and stretched is called the “temporary stretch cavity” or TSC. The space left by tissue that is cut or crushed and physically removed from the target is called the “permanent cavity” or “crush cavity.” At impact velocities below 2,000 fps, human tissue is extraordinarily elastic and simply stretches before snapping back to place with little real physical damage. The exception is brain and liver tissue, with is not particularly elastic. At velocities over 2,000 fps the TSC exceeds the elastic limit of human tissue and permanent tears are created, which contribute to the permanent cavity.
Rifles are rifles and pistols are pistols:
Not many handguns come anywhere near this velocity, though. That means that handgun wounding is the result of the crush cavity alone. “Hydrostatic shock” and other such nonsense is not a factor. The crush cavity is determined by the average expanded diameter of the projectile and the depth of penetration. Remember that a projectile MUST penetrate at least 12” to be useful for defense.
Modern, jacketed hollow point defense ammunition for handguns produces expanded projectiles that vary only slightly between calibers and penetrate similarly as well. It is true that larger caliber bullets tend to expand to a slightly larger diameter but not by as much as you might expect. The slight difference in expanded diameter results in very little real difference in tissue damage. Theoretically, this principle also applies to higher velocity handgun cartridges like the .357 magnum and 10mm. 125 gr .357 mag has a typical velocity of about 1,450 fps, which is well below that 2,000 fps threshold that is required for TSC to contribute to wounding. So why does .357 mag 125 gr JHP have such a reputation as a “man stopper”?
I have an entirely unprofessional opinion as to why this might happen. Many attacks stop, not because a person was physically incapacitated, but because they decided to stop for one reason or another. They might decide to stop because of pain or because of the idea of getting shot. We’ve all seen the movies and TV shows where someone gets shot and immediately crumples to the floor, lifeless. Sometimes bad guys just stop because that’s what you’re supposed to do when you get shot. Some people have referred to this as a “psychological stop.”
Take a look at these gelatin tests. You can clearly see that the blocks are hit harder by 10mm than they are by 9mm.
10mm Underwood 165 gr Gold Dot:
9mm Federal 124 gr +P HST:
As you can see, the block hit by the 10mm is visibly lifted into the air quite a bit. The crush cavity produced by each is not dramatically different but 10mm has a lot more energy delivered to the target. That energy is mostly spent in stretching elastic tissue (temporary stretch cavity) which snaps right back into place as mentioned above. That doesn’t produce any significant wound and therefore shouldn’t contribute to incapacitation. But if I punch you in the stomach, that won’t produce any significant wound, either. I’m no Mike Tyson, after all. It will hurt, though. A lot. Probably take a little vinegar out of you, too.
That’s my hypothesis: that some particularly energetic handgun cartridges “thump” a bad guy enough that he really feels getting shot. Maybe that blunt trauma can contribute to a psychological stop. Is that enough to justify the dramatically greater recoil and muzzle blast? That’s not my place to figure.
While my opinion about the blunt trauma is my own, entirely unprofessional opinion, the facts I relate above are solid, proven principles based on observations made by professionals. Don’t take my word for it, though. Do the reading for yourself.
Let us know in the comments what views you have on stopping power.