9mm vs. .40 .vs .45: The Definitive Article On Caliber Performance

For decades, handgun shooters have argued over what is the most effective handgun caliber; a discussion that will likely continue well into the future.

The debate generally centers on three options, the 9mm, .40 S&W and .45 ACP.  Which has the most stopping power?

Which is best for home defense? These are just some of the questions that fuel this argument. Although you can find pieces claiming that each is superior, I set out to write this article as the definitive guide to which caliber is truly the best.

Clearly one is more powerful, one is more accurate, and one is more deadly…right?

As someone who thoroughly enjoys shooting, I have fired many rounds of different calibers while using a variety of weapons systems.

In my experience, I enjoy firing a .40 S&W handgun; finding myself to be far more accurate with it than with a .45 caliber weapon.

I do not shoot 9mm handguns very often, because they don’t have enough stopping power to be practical; a point I will explore shortly.

In addition, most military units and law enforcement agencies use either .40 or .45 caliber pistols. Certainly, their judgment must count for something.

Of course, I went into this article to test all three calibers fairly and scientifically, but I did have a good idea of what I would find before I began.

I expected the 9mm to be more accurate, as it is the least powerful and more controllable round.

I anticipated that the .45 ACP rounds would do the most damage and penetrate the deepest, but I also thought it would be the least accurate.

Finally, I presumed that my personal favorite; the .40 S&W, would be that sweet spot in the middle; the perfect mix of accuracy and power. I could not have been more wrong; or more surprised, by the results.

Before we get into firing the weapons, let’s go through some math.

The energy released by each round is measured in foot-pounds and is scientifically calculated by the manufacturer:

• 9mm+P 115 grains: 323 foot-pounds
• .40 S&W 140 grains: 390 foot-pounds
• .45 ACP +P 185 grains: 411 foot-pounds
  
  

As you can see, the .45 ACP has approximately 27% more energy than the 9mm while the .40 S&W is almost dead in the middle. No big surprise, right?

Now let’s look at a measure that many experts believe is a better representation of a bullet’s power; momentum.

Momentum is not measured in foot-pounds, but rather pounds-feet per second (lb-ft/s).

• 9mm+P 115 grains: 18.5 lb-ft/s
• .40 S&W 140 grains: 22.4 lb-ft/s
• .45 ACP +P 185 grains: 26.4 lb-ft/s
  
  

Again, we find what we might expect – the largest caliber has a whopping 43% more momentum than the smallest caliber and the .40 S&W is once again comfortably in the middle.

So why continue with this article?

Why continue any testing at all, when we can see the scientific results right in front of us?

As you keep reading, you might discover that this is where the expected results end and where the surprises begin.

We now know how the different calibers compare on paper, but how does that translate into real-world performance?

Let’s start by firing each caliber at a piece of ballistics gel at a distance of ten feet.

After five shots of each caliber are fired, we will look at three different factors: penetration depth, size of the wound channel, and size of the expanded projectile.

After 5 shots of each caliber were fired into a block of ballistics gel from a distance of ten feet, we discover something unexpected; all three projectiles penetrated to nearly matching depths and produced nearly identical wound channels.

As seen in this photograph from testing done by the U.S. Federal Bureau of Investigation; there are slight differences in penetration and size of the wound channel yet those differences are almost imperceptible and irrelevant in the real world.

Maybe even more surprisingly, the size of the expanded projectiles are nearly identical.

Of course, the .45 round is slightly larger than 9mm rounds, but even in their expanded state, the difference between them is only around one millimeter.

Remember at the beginning of this article when I said that I didn’t shoot 9mm very much and that I intended to explore that reasoning further?

My early assumptions could not have been more wrong.

During my research and testing for this article, I accidentally created the definitive article that solidly ends the debate on which round is superior.

The answer is: there is no answer! With the state of modern ammunition, there is no meaningful difference in the performance of these calibers.

In fact, there was also a study done that looked at military and law enforcement reports concerning victims and suspects shot by handguns which used the data to analyze the various calibers for comparison.

The results were entirely consistent with the testing.

• Average number of rounds until incapacitation: 2.45, 2.36, 2.08
• Percentage of people not incapacitated: 13%, 13%, 14%
• Percentage incapacitated by one shot (torso or head hit): 47%, 52%, 51%
  
  

The data indicates that all three calibers had nearly identical properties when it came to real-world situations.

They all averaged more than 2 rounds to incapacitate someone, and nearly all the statistics are well within a reasonable margin of error.

The very slightest of edges goes to the larger ammunition for stopping people with one shot. This is likely attributed to the extra millimeter of expansion occasionally nicking something vital.

I’m not exactly an “authority” on ammunition performance.

Sure, I can read some data and analyze some testing, but that hardly qualifies me as an expert. Luckily, you don’t have to take my word for it.

I think it is fair to consider the FBI to be a credible authority on firearms.

After conducting their own studies, they transitioned all of their agents to 9mm firearms. In fact; in their agency memo detailing the specifics of why they switched, the FBI’s Training Division determined:

“9mm Luger now offers select projectiles which are, under identical testing conditions, outperforming most of the premium line .40 S&W and .45 Auto projectiles tested by the FBI”

They also found “There is little to no noticeable difference in the wound tracks between premium line law enforcement projectiles from 9mm Luger through the .45 Auto”.

A major takeaway from the FBI’s findings is the clear message that it’s all about the ammo.

Testing makes it clear that the ammunition you use, regardless of caliber, is far more important than the caliber of the weapon itself. 

So the true answer to which caliber handgun is best is simple: whichever caliber you shoot most accurately.

A shot in the head from any of these rounds would be fatal, and a center-mass shot from any of them would do almost identical damage.

So find a firearm you like, practice with it, and it will serve you well.