It is one of the internet’s basic truths that if you want to start an argument about terminal ballistics, ask people whether 9mm or .45 is the better caliber.
Go ahead and drop your answer in the comments now, just to get things started. And don’t say .40 or 10mm, you instigator.
This article isn’t really about the debate between these calibers, but rather the science that supports people’s arguments. Today we’re starting the conversation about ballistics. Specifically, we’re talking about terminal ballistics. The other areas, internal and external, are for another article.
So why are we hitting this subject? Part of marksmanship is knowing not only how to aim and fire the rifle from a stable position, but what the bullet will do during flight and on impact. Generally speaking, target shooters are less concerned about terminal ballistics than hunters or defensive-minded shooters.
Why This Matters
Target shooters usually care less about terminal ballistics than hunters or defensive shooters. You see, competitors only need the bullet to impact a desirable spot. Once the hole is punched or the gong is rung, then they don’t really care what happens next. For that reason, they are much more focused on what the bullet does in flight, and favor designs that offer better external ballistics at the cost of terminal performance.
But if you need that bullet to not only hit what you needed but also cause enough tissue damage to “put the target down.” Then you care very much about terminal ballistics and should choose bullets that have favorable characteristics.
How Bullets [Don’t] Wound and Kill
This is an interesting, though complicated topic. Knowledge of how bullets wound targets evolved over the years. The ideas we operate under today are vastly different than what we thought 100 years ago, even though the technology hasn’t changed all that much.
I’ll get to the history of terminal ballistics in a second, but let’s just get something out of the way first. A bullet kills via two methods, and only two methods:
- Destroy something vital in the central nervous system (brain or spinal cord) so that electrical impulses are no longer generated or carried
- Drain enough blood from the body (via holes) so that oxygen no longer effectively circulates
The real trick is in how we get to one of these two outcomes. So let’s talk history.
A Brief History of Wound Research
The meat of this research goes back to the 1870s and the work of Theodor Kocher. Born in Switzerland in 1841, Theodor Kocher rose to the rank of Colonel in the Swiss Militia. By 1872, he earned a position as a professor of surgery in Bern.
Kocher was particularly interested in the evolution of terminal ballistics as small arms transitioned from the traditional spherical musket ball to the more devastating minié ball used during the American Civil War and other conflicts around the world.
He was the first to formalize a few theories that would have lasting impacts. His primary wounding channels were:
- Deformation of the bullet which transferred more kinetic energy
- Bullets dragging surface contaminants into the wound
Let’s talk about each of these a little more, since they become very important later on.
Kocher was the first to formally test this hydraulic pressure theory. He showed that it had merit by shooting into sealed boxes filled with water. An article from the American College of Surgeons has a nice writeup on Kocher’s experiments.
In short, Kocher believed that a significant driver of rifle wounds was this pressure causing the stretching and destruction of tissues inside the body.
Bullet Deformation and Kinetic Energy
Another theory was that the elongated shape of the minié ball meant that it deformed as it impacted. This deformation led to a greater kinetic energy transfer from the bullet in flight to the target.
Kocher worked with Col. Eduard Rubin of the Swiss Federal Ammunition Factory and created the first full-metal-jacket bullet. Kocher’s reasons stemmed from a desire to inflict less damage to the target by limiting the amount of bullet deformation. Colonel Rubin saw that these FMJ bullets had higher velocity, accuracy, and came at a lower weight.
It appeared to be a win/win.
This was actually the basis for the Hague Conventions, which enforced the use of FMJ bullets rather than expanding or soft-pointed “dum dum” bullets. The Americans and the British were the only two nations to vote against the measure.
The Americans had fought against the new style FMJ bullets during the Spanish-American War, and found the decreased lethality concerning (though appreciated the increased range and accuracy). The British, on the other hand, were frustrated by the lack of performance they perceived with the FMJ bullets while fighting in India.
The soft-point “dum dum” type of bullet they came to favor came from that conflict, where they snipped the tips off of FMJ bullets to expose the soft lead core and improve deformation.
This is less relevant to our discussion today since infection is something that causes problems later on and doesn’t immediately stop a threat.
Kocher proved that bullets, especially wider flatter ones, could drag harmful bacteria into a wound with them. This bacteria could come from anywhere, such as the skin or clothing, but that’s not why this was an important discovery.
At the time, most of the world assumed that the temperature of the bullet in flight was high enough to sterilize the surface of the projectile.
The Le Garde-Thompson Tests
To execute the tests, they shot several livestock animals with handguns in a variety of calibers. Some of these included the 9mm Luger, .45 ACP, .38 Long Colt, and .455 Webley.
Their conclusions were pretty straight forward (emphasis mine):
The board was of the opinion that a bullet, which will have the shock effect and stopping effect at short ranges necessary for a military pistol or revolver, should have a caliber not less than .45. … None of the full-jacketed or metal-patch bullets (all of which were less than cal. . 45) showed the necessary shock effect or stopping power for a service weapon….
We are not acquainted with any bullet fired from a hand weapon that will stop a determined enemy when the projectile traverses soft parts alone. The requirements of such a bullet would need to have a sectional area like that of a 3-inch solid shot the recoil from which when used in hand weapons would be prohibitive. …
Finally the Board reached the conclusion that the only safeguard at close encounters is a well-directed rapid fire from nothing less than a .45-caliber weapon. With this end in view soldiers should be drilled to fire at moving targets until they have attained proficiency as marksmen.
I want to draw your attention to the “shock effect” and “stopping power” statements. These are important later on.
The big takeaway from this experiment, according to a doctoral thesis by Nicholas Maiden for The University of Adelaide in Australia, was that the most important element of ballistic wounding was the permanent cavity. This is the tissue actually cut, crushed, and destroyed as the bullet passes through.
1930: The Work of R.H. Kent
Robert Kent of the Aberdeen’s Ballistic Research Laboratory published a little-known report in 1930. I’ve covered this particular report in before, so I won’t go into the gritty details gain.
The big thing to take away is that everyone still believed that kinetic energy transfer was a primary terminal ballistics wounding mechanism for rifles. Kent’s theory was that a smaller and faster projectile could transfer an equivalent amount of kinetic energy to a target as a larger slower projectile.
If this was true, he surmised, then soldier’s could carry more ammunition, lighter rifles, and be more effective on the battlefield than using traditional full-sized battle rifles.
I’m going out on a limb here and hypothesizing that this was also a desirable path as long as everyone was working within the bounds of the Hague Conventions. If a smaller FMJ bullet was as effective from a wound standpoint as a heavier 30-06 at combat distances, then why carry the heavier bullet?
If you’ve read my series on the Small Caliber High-Velocity program, then you know that this theory ultimately prevailed and resulted in the US Military adopting the M16 rifle chambered in a lightweight 55gr projectile known as M193. But it all hinged on the kinetic energy transfer theory, which turns out to be incorrect.
Where it All Goes Wrong
Now things get interesting.
You see, from at least the late 1800s through the Vietnam War, everyone assumed the kinetic energy transfer model was correct. The “shock” of getting hit by a fast-moving projectile and absorbing its kinetic energy contributed to “stopping power” and made rifles more effective.
Early reports of experimental AR-15s from Vietnam talked about “devastating” damage and wounds. Dramatic and graphic photos publicized by the Swiss government showed photos of damage by the M16. They claimed it was inhumane to use in warfare since it did more damage than the 7.62 NATO cartridge that complied with the Swiss-derived Hague Conventions.
But where was the proof?
Enter Martin Fackler
Dr. Fackler served as a surgeon and a Colonel in the US Army Medical Corps. He worked as a field surgeon in Da Nang during Vietnam, and saw his fair share of bullet wounds. During this time, noticed a disconnect between what was being said about rifle ballistics, and particularly the 5.56, and what he actually observed in the field.
Fackler used a combination of logic and calibrated ballistic gel to suss out the real wounding mechanisms of rifle bullets. In a 1987 paper titled What’s Wrong With the Wound Ballistics Literature, and Why he dispels several of the commonly held beliefs and myths surrounding bullet wounds.
Terminal Ballistics Myths
To start, Fackler emphasizes that there are only two mechanisms for wounding:
- Temporary cavitation: tissue stretched and temporarily displaced
- Permanent wound channel: tissue cut and crushed as the bullet passes
The bottom line here is that the theory of kinetic energy transfer is wrong. At worst it is totally irrelevant, at best it is an inconsistent wounding method and should not be relied upon.
Another myth is the supersonic shockwave as the bullet penetrates. A lot of folks assumed this was another wounding mechanic of SCHV projectiles. Fackler points out the logical fallacy here:
The “devastating” wounds documented by early AR-15s? There was nothing scientific about the reports. Nobody actually compared it to a the results of a full-sized cartridge.
The “inhumane” findings of the Swiss government? They were intentionally misleading, using undersized pigs to show relative damage and selectively choosing the worst damage. It was a politically-motivated stunt.
I could go on, but you get the idea.
How Bullets Wound and Kill
This brings us to the modern age, where we know a lot more than we did when Kocher started his experiments in the late 1800s.
A bullet, any bullet, wounds effectively in only one of two ways.
Permanent Wound Channel
The permanent wound channel is the tissue cut, crushed, and displaced as the bullet passes. If this wound channel passes through some vital organ or tissue, like the brain or heart, then death occurs very quickly. The problem is that these vital areas are relatively small and hard to hit.
Alternatively, you could poke enough holes in other tissue to let blood flow out of the circulatory system. If you hit a major blood vessel, like the aorta or femoral artery, then this blood loss occurs very quickly in as little as a single shot. But, it usually takes more than one hit to poke holes in all of these places.
That’s the reason for aiming at center mass. There’s a higher probability of hitting areas with a lot of blood flow.
This is also why firing only a single shot is a bad idea in a life or death situation.
You fire until the threat stops.
Temporary cavitation is a real thing. But a lot of people have overblown its effect.
Without getting into the physics of it, imagine what happens as you throw a rock into a pond. The inertia of the rock penetrating the water causes a wave that ripples out. The same thing happens to live tissue as a bullet penetrates it. The inertia of the bullet temporarily moves tissue out of the way.
Since tissue is elastic, and mostly made of water, it quickly rebounds back to its original position. Fackler points out that you really shouldn’t think of this as any more than blunt trauma. Most tissues in the body are stretchy and aren’t dramatically affected by this temporary cavity. But others, such as the liver and kidneys, are more susceptible.
This is the real area of terminal ballistics that Fackler is known for. While he is hard on the old ways of thinking, he demonstrated that the worst wounds come from the fragmentation of the bullet.
If you recall my article on rifle twist rates, I talked about the aerodynamic forces working on a projectile in flight. The shape of a modern rifle bullet puts the center of pressure in front of the center of mass. That means that a bullet insufficiently stabilized is prone to tumble.
When a rifle bullet impacts soft tissue, reducing its velocity and spin rate, the bullet becomes unstable and begins tumbling inside of the body. If the jacket is thin enough, the drag forces of traveling through tissue sideways tend to break the bullet apart. When this happens, pieces of the jacket and lead core fly off in various directions.
This is fragmentation.
When you combine the shredding effect of fragmentation with the intense blunt trauma and stretching effect of temporary cavitation, you enable dramatic wound channels. Think of it like a rubber band that you nicked with a knife. What used to be easily stretchable will now rip and tear.
Shattered bone fragments can have the same effect, perforating surrounding stretchy tissue until it ruptures rather than stretches.
If both fragmentation and cavitation occur, you make the permanent wound channel much more intense.
But that’s a big if.
All rifle bullets do this to a degree, but smaller lighter bullets tend to do it better. Even then, achieving this kind of synergistic effect isn’t 100% reliable, which is why it’s common to fire more than one shot.
Putting it Together
When you look at all of this, you see why handguns are much less effective compared to rifles.
Handgun bullets don’t have the inertial power to trigger large temporary cavities, nor do they have the aerodynamic properties to fragment. A handgun relies entirely on shot placement and the permanent wound channel for damage. Expanding ammunition increases the diameter of that wound channel and the probability that you put a hole in something important- but not by much.
Expanding hollow-point ammunition doesn’t make up for poor marksmanship.
Rifles do both. Soft-point expanding ammunition works well on animals because it causes both a larger temporary and a wider permanent wound channel. Of course, that’s assuming it doesn’t fragment, which we typically don’t want in a hunting round because it could ruin the meat.
A Word of Caution
Here’s the deal, looking at all of this stuff is fun and interesting, at least to me, but it’s also based on a lot of theory and other people’s experiences. At the end of the day, seek out some professional training and advice on what works for you and your situation.
I’ve always liked this video of Clint Smith at Thunder Ranch laying down some “real talk.” Be aware of some harsh language in case you’ve got speakers turned up.
This is just the start of a longer discussion about ballistics.
The big takeaway here is that it’s an evolving science. I made a lot of use of Fackler’s work, but realize his work is based on his experiences. There are others in the field who disagree with him on the relevance of shockwaves and other effects that Fackler discounted.
Stay safe, and I”ll see you next time.