Just what is the best self-defense caliber?

The question with no definitive answer.

Let’s say you locked 100 “gun experts” in a room. You tasked them to define what is the best self-defense caliber. You gave them 8 hours to come up with the answer. At the end of the 8 hours, you most likely would have at least 7 different answers and a few bloody noses.  

I decided to do my own research. Every source I read has different recommendations. Some like big heavy bullets. Some like lighter, faster bullets. At one end of the debate, you have “You only need one hit with a .45 to stop the attacker” position. On the other end, you have “one-hit with a .22 is better than 7 misses with a .45” position.

Both ends are firmly committed to their position. There isn’t any consensus. The more I read, the more confused I get.

There is more to the answer than just caliber!

I recently ran across an article by Greg Ellifritz. While this article is a little dated (written in 2011), it cleared up much of my confusion. 

Let’s wade through the data to see why the choice is so difficult. Hopefully, by the end, you will be armed with what you need for your choice of a self-defense round.

Stopping Power vs. Lethality

Stopping power is the ability of a weapon to cause a target (human or animal) to be incapacitated or immobilized.

Stopping power contrasts with lethality in that it pertains only to a weapon’s ability to make the target cease action, regardless of whether or not death ultimately occurs.

Clears everything up; right? Not for me. I had to dig deeper.

Which ammunition cartridges have the greatest stopping power is a much-debated topic.

Stopping power is related to the physical properties and terminal behavior of the projectile, and the wound location. This means the issue is complicated and not easily studied.

Higher-caliber ammunitions usually have greater muzzle energy and momentum. Because of this, they have been widely associated with higher stopping power. However, the physics involved are multifactorial, with caliber, muzzle velocity, bullet mass, bullet shape, and bullet material all contributing to the ballistics.

Despite much disagreement, the most popular theory of stopping power is that it is usually caused not by the force of the bullet. Instead, it is a result of the wounding effects of the bullet, which are typically a rapid loss of blood causing a circulatory failure, which leads to impaired motor function and/or unconsciousness.

The “Big Hole School” and the principles of penetration and permanent tissue damage are in line with this way of thinking. The other prevailing theories focus more on the energy of the bullet and its effects on the nervous system, including hydrostatic shock and energy transfer, which is similar to kinetic energy deposit.

It more than the calibar.

Here are things we must consider:

  • Muzzle velocity
  • Bullet weight
  • Bullet construction
  • Accuracy
  • One-shot stop percentage
  • The shooter’s skill level

Muzzle velocity & bullet weight – Our first two items are based on physics. Kinetic energy is calculated by multiplying one-half of an object’s mass times the square of its velocity ( 1/2mv2). Based on this calculation, our best choice for self-defense would be a .44 magnum. It would have the greatest kinetic energy. However, we would be foolish to stop our discussion here. 

Bullet construction – This discussion revolves around Full Metal Jacket vs. Jacketed Hollow Point.

FMJ ammo gets its name from the jacket that covers the entire bullet. This covering is usually a copper or copper and steel alloy designed to reduce the amount of lead residue in the barrel after firing. The most important thing to note is that FMJ ammo remains whole and jacketed even after hitting its target.

JHP ammo follows a similar construction to FMJ. The difference is, a JHP has a hole in the tip of the bullet, giving it a hollow center. When a JHP makes contact with the target, the bullet expands like an umbrella which creates a cavity in the soft tissue. JHPs don’t usually go through their target, but they do cause more damage. On impact, the energy transfers from the bullet to whatever stopped it, slowing it down drastically and leading to devastating damage.

Based on this calculation, our best choice for self-defense would be a .44 magnum with a JHP bullet. However, we would be foolish to stop our discussion here. o

Accuracy – Here is where our selection becomes complicated. What percentage of your hits would be in the head or torso. How does this affect stopping power? For example, if one caliber had a huge percentage of shootings resulting in arm hits, we may expect that the stopping power of that round wouldn’t look as good as a caliber where the majority of rounds hit the head. This starts to place some issues with our choice for self-defense as a .44 magnum with a JHP bullet. Looking at Greg Ellifritz’s data, the 9mm had the highest hits per shot. Even the .380 has a better average than the .44 magnum. This seems to shift our choice to the 9mm.

One-shot stop percentage – the number of incapacitations divided by the number of hits the person took. in Greg Ellifritz’s study, he only included hits to the torso or head in this number so accuracy places a part in this discussion.

Gleaning more from Greg Ellifritz’s study, He thinks the most interesting statistic is the percentage of people who stopped with one shot to the torso or head. There wasn’t much variation between calibers. Between the most common defensive calibers (.38, 9mm, .40, and .45) there was a spread of only eight percentage points. No matter what gun you are shooting, you can only expect a little more than half of the people you shoot to be immediately incapacitated by your first hit.

Another data piece that leads me to believe that the majority of commonly carried defensive rounds are similar in stopping power is the fact that all four have very similar failure rates. If you look at the percentage of shootings that did not result in incapacitation, the numbers are almost identical. The .38, 9mm, .40, and .45 all had failure rates of between 13% and 17%.

The shooter’s skill level – This is the hardest factor in our selection to quantify. Regardless of the caliber, the novice is less likely to have the hit rate of an experienced shooter. On the other hand, the experienced shooter might be better served with a larger caliber firearm.


OK, here is the part where I am supposed to tell you the BEST choice of a self-defense round. Sadly like our 100 experts, I cannot give one choice.

None is a death ray, but most work adequately…even the lowly .22s. I’ve stopped worrying about trying to find the “ultimate” bullet. There isn’t one. And I’ve stopped feeling the need to strap on my .45 every time I leave the house out of fear that my 9mm doesn’t have enough “stopping power.” Folks, carry what you want. Caliber really isn’t all that important.

If you want to be prepared to deal with someone who won’t give up so easily, I would skip carrying the “mouse gun” .22s, .25s, and .32s. My personal choice is a 9mm loaded with JHP. 

Head shots = 75% immediate incapacitation
Torso shots = 41% immediate incapacitation
Extremity shots (arms and legs) = 14% immediate incapacitation.

No matter which caliber you use, you have to hit something important in order to stop someone!

Oh, if you are a novice shooter, your best choice today may not be your best choice after some training and range time. 

For those of you that are skilled shooters, you can be mad at me for one picking your favorite round. After all, the choice is personal. 

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