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.
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. I’m also focusing primarily on how we got to the .223/5.56 and why it matters.
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 does 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 don’t usually care about terminal ballistics compared to hunters or defensive shooters. For target shooters, once the bullet punches a hole or rings the gong, what happens next is immaterial. For that reason, they focus much more on what the bullet does in flight. Target shooters, especially at long range, favor designs that sacrifice terminal performance in favor of improved external ballistics.
However, if you need that bullet to not only hit the target 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 a complicated topic and 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 cannot effectively circulate
The trick is in how we get to one of these two outcomes. So let’s talk history.
A Brief History of Wound Research
Let’s start in the 1870s with 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 spherical musket balls to the more devastating Minié ball used during the American Civil War and other conflicts around the world.
He formalized several theories that would have lasting impacts. According to Dr. Kocher, the 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.
Dr. Kocher was the first to formally test the hydraulic pressure theory. He demonstrated its merit by shooting sealed boxes filled with water. An article from the American College of Surgeons has a nice writeup on Kocher’s experiments.
In short, Dr. Kocher believed that this pressure wave stretching and destroying tissue was a significant driver of rifle wounds in the body.
Bullet Deformation and Kinetic Energy
Another theory was that the elongated shape of the Minié ball led to bend and deform as it impacted. This deformation led to a greater kinetic energy transfer from the bullet in flight to the target.
Dr. Kocher worked with Col. Eduard Rubin of the Swiss Federal Ammunition Factory and created the first full-metal-jacket bullet. Dr. 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.
Dr. 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:
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.
Pay 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 take away is that everyone still believed that kinetic energy transfer was a primary terminal ballistics wounding mechanism for rifles. Kent theorized 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 soldiers could carry more ammunition, lighter rifles, and be more effective on the battlefield than using traditional full-sized battle rifles.
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
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 photos publicized by the Swiss government showed graphic wounds created 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, he noticed a disconnect between what was being said about rifle ballistics, particularly the 5.56, and what he actually observed in the field.
Dr. 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, Dr. Fackler emphasizes that there are only two mechanisms for wounding:
- Temporary cavitation: tissue stretched and temporarily displaced (as proposed by Theodor Koch)
- Permanent wound channel: tissue cut and crushed as the bullet passes
According to Dr. Fackler’s work, 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 surrounds the supersonic shockwave as the bullet penetrates. Many people 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-powered rifle 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.
How Bullets Wound and Kill
This brings us to the modern age, where we know a lot more than we did when Dr. 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, poking enough holes in other tissue allows blood to 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, as theorized by Dr. Koch, is a real phenomenon. However, the effect is overblown.
Imagine throwing 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 to its original position. Dr. 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 area of terminal ballistics that Dr. Fackler is known for. 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, dramatically reducing its velocity and spin rate, the bullet becomes unstable and begins tumbling. 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.
This tumbling and fragmentation effect takes place some distance after the initial impact, typically 12-15 inches. With a human combatant, that means that fragmentation could happen inside the body.
Fragmentation and Terminal Ballistics
When you combine the possible 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 due to their construction. Even then, achieving this kind of synergistic effect isn’t 100% reliable. Which is why it’s so common to fire more than one shot.
Also, since fragmentation is related to the dramatic deceleration of the bullet, it helps to have the bullet moving at a higher velocity upon impact. This is why barrel length has an impact on the “optimal” effective range of the .223 projectile.
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. Rifles do both.
A handgun relies entirely on shot placement and the permanent wound channel for damage. Expanding ammunition only slightly increases the diameter of that wound channel and the probability that you put a hole in something important..
Expanding hollow-point ammunition does not make up for poor marksmanship.
With rifles, soft-point expanding ammunition works well on animals because it causes both a larger temporary and a wider permanent wound channel. 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
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 Dr. 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 shock waves and other effects that Dr. Fackler discounted.
Stay safe, and I’ll see you next time.