9mm vs 40 S&W vs 45 ACP & “Stopping Power”

9mm vs 40 S&W vs 45 ACP Stopping PowerThe 9mm vs 40 S&W vs 45 ACP  debate has been raging for a long time.  I can’t solve it for you, but I can give you the information you need to make an informed decision.  But we need to jettison some pseudo-science first.

Kinetic Energy does not matter. 


It has exactly zero effect of a bullet’s deadliness.

Don’t believe me?

A 490 grain Broad-head arrow traveling at 225 Feet Per Second (FPS) has a kinetic energy of 55 ft-lbs. A 1 pound gel filled bag launched at 60 FPS has a Kinetic Energy of 55 ft-lbs.

Exact same energy, but which is more lethal?

Its very simple and easy to understand how an attacker can be incapacitated.   But it’s not with some mythical force called “stopping power” or “knock down power”.  Consider this: Can you measure “Stopping Power” or “Knock Down Power”?

Seriously, how many “Stopping Powers” or “Knock Down Powers” does a 45 ACP have?  How about a 9mm or 40 S&W?

I’m not the only with this opinion either.  The FBI switched back to 9mm from 40 S&W a couple years back.  They released a report justifying the switch which is well worth a read.

Studies of “stopping power” are irrelevant because no one has ever been able to define how much power, force, or kinetic energy, in and of itself, is required to effectively stop a violent and determined adversary quickly, and even the largest of handgun calibers are not capable of delivering such force. Handgun stopping power is simply a myth.

(Bold emphasis theirs, red emphasis mine.)


It doesn’t matter if it’s 9mm, 40 S&W, or 45 ACP; they all do damage the same way.  So before I get into comparing and contrasting 9mm vs 40 S&W vs 45 ACP, lets spend a minute talking about how bullets ACTUALLY do their damage.


Wound Ballistics Basics

(try saying that five times fast)


According to the FBI report Handgun Wounding Factors and Effectiveness, there are only two ways a bullet can do damage:

#1.  Permanent Cavity. (The tissue the bullet touches directly, which it crushes into oblivion.  Basically the hole it leaves.)

#2.  Temporary cavity. (Basically the tissue the bullet damages, but does not touch. Read my “Stopping Power” and The Simple Truth of Terminal Ballistics article for more details.)

Here’s the bad news: most handgun bullets can only create a damaging permanent cavity (hole).  Rifle bullets can create a damaging temporary cavity and are far more deadly.  But unless you have a rifle or very powerful handgun, don’t even worry about a damaging temporary cavity.  (there are a few exceptions, which we will discuss lower down)

Pistol bullets only poke holes.

That’s it.

Here’s the FBI on the matter:

Handgun stopping power is simply a myth

The single most important factor in effectively wounding a human target is to have penetration to a scientifically valid depth (FBI uses 12” – 18”)

Clint Eastwood Do you feel lucky punk

Yeah it’s a great line about a 44’s power. But Hollywood got something about guns wrong… Again.  Surprise, surprise.

Pistol bullets – even large ones like the .44 Magnum – literally CAN’T knock a person off their feet. Smaller ones like 9mm and 40 S&W don’t even have a prayer of doing it.

They just can’t.

To inject some science into that statement, let’s look at the Newton’s Third Law of motionFor every action, there is an equal and opposite reaction.”  That means that all the force the bad guy feels is also felt by the shooter (in the form of recoil).

Therefore, If a bullet can knock the bad guy down, it would also knock the shooter down. (though the forces might feel different because the weight of the gun reduces the force the shooter feels.)

Even 45 ACP bullets can’t knock someone off their feet.  If you break major bones, they may be unable to continue standing and then fall down.  But they won’t be “knocked off their feet”.  Worse, they might not be stopped, or even slowed down.

Don’t believe me?

Two suggestions: watch a video of someone shooting 45 ACP into a block of ballistics gel.  The block of gel weighs around 20 pounds, and the 45 ACP can’t make it go flying.  If it can’t move a ~20 pound block of gel, what makes you think it can “knock down” a 150-300lb man?

Second, I suggest reading this article recounting a police officer’s encounter with a bad guy:  Why One cop Carries 145 Rounds of Ammo on the Job.

No really, go read it.

I’ll wait here.

The officer’s pistol was a Glock 21 chambered in 45 ACP and the officer himself was:

A master firearms instructor and a sniper on his department’s Tactical Intervention Unit, “I was confident at least some of them were hitting him, but he wasn’t even close to slowing down,”  (emphasis added)

And this one too:

I thought I was hitting him, but with shots going through his clothing it was hard to tell for sure. This much was certain: he kept moving and kept shooting, trying his damnedest to kill me.” In this free-for-all, the assailant had, in fact, been struck 14 times.” (emphasis added)

Here’s the clincher:

no evidence of drugs or alcohol was found in his system.

Pistol bullets can only poke holes; they can’t knock people down.

(and don’t forget, that’s the FBI’s professional opinion after untold hours of research and testing)

Movies have been getting this wrong for years.  A western draw is a perfect example.  The slower shooter always stops like he’s struck by a bolt of lightning. For the most part, that’s pure Hollywood fantasy.  (unless the bullet hits either the brain or spinal cord)


So What Does it Take to Stop a Bad Guy?

Answer: You have to poke the holes in the right places.

In the 9mm vs 40 vs 45 debate, you can’t forget this simple fact:

The only way to instantly incapacitate an attacker is to destroy or disable the brain. If you can hit the brain, it’s lights out. (The officer ended the gunfight with a few shots to the assailant’s head.) However, the head is a small and easily missed target.

Because the head is a small target, conventional wisdom says aim for high center of mass.

For once, conventional wisdom isn’t completely wrong.

You need to disable the brain to force an attacker to stop.   The only real way to do that (other than hitting the head or spinal cord) is by poking enough holes in arteries that they blackout from blood loss.

There’s a whole host of arteries and veins – not to mention the heart –  that are protected by the rib cage.  Hit enough of them, and their blood pressure will lower to the point of forcing unconsciousness. However, even if you put a bullet through the heart they will still have 6-10 seconds of consciousness left.

6-10 Seconds in a LOT of time in a gunfight.

It’s plenty of time for them to return fire, attack you with a knife, or swing a baseball bat with bone breaking force.  To make them stop, you need to disable the brain.  To do that without hitting it directly, you need to hit large concentrations of blood bearing organs and/or arteries.

The best place to do that is  high center of mass.

However, It requires proper shot placement to incapacitate ANY bad guy.  Hitting the bad guy in the pinky finger with a 500 S&W Magnum is less effective than hitting them in the head with a 22LR.

To back up these claims, I’ll quote the FBI justification for returning to 9mm:

Shots to the Central Nervous System (CNS) at the level of the cervical spine (neck) or above, are the only means to reliably cause immediate incapacitation. In this case, any of the calibers commonly used in law enforcement, regardless of expansion, would suffice for obvious reasons. Other than shots to the CNS, the most reliable means for affecting rapid incapacitation is by placing shots to large vital organs thus causing rapid blood loss. Simply stated, shot placement is the most critical component to achieving either method of incapacitation.

(emphasis mine)

I’m not just making this stuff up.


Now that we know how to stop a Bad Guy, back to the debate…

In my opinion, 9mm vs 40 S&W vs 45 ACP doesn’t matter too much because they all poke holes around the same size.  Yeah I know that sounds silly, but it’s true.  The FBI Justificaiton for going  back to 9mm backs this fact up again.

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

As further proof, check out the picture below.

Those are Winchester T-series hollowpoint bullets after expansion.  They are commonly agreed as one of the best jacketed hollow point bullets around.

Notice how close the expansion is.

The difference between the 9mm and the 45 ACP is only .12 inches. Basically one eighth of an inch.  The 40 S&W splits the difference exactly.

Now, lets say you were in a self defense scenario and hit the bad guy.  Good for you.  But lets say the bullet missed something vital, but only missed it by a tiny little bit.

If you were shooting a 45 ACP that landed in the exact same place as a 9mm, you’d only be half the diameter – or 0.060 of an inch – closer to the vital zone than a 9mm.

1/16 of one inch.  That how much closer you’d be with a 45 ACP vs a 9mm.

With a 40 S&W, you’d be 0.03 of an inch closer than a 9mm. That’s only 1/32 of an inch (less than a millimeter) in a 9mm vs 40 S&W.

Yes I know, that’s only one type of bullet.  So how about  larger sample size?

Lucky Gunner did an extensive ammo test with over 100 different types of self defense hollow points. They listed the raw data along with gel pictures and video.   I added the average expansion numbers for 9mm, 40 S&W, and 45 ACP and here’s what the number’s say.

  • 9mm Average Diameter: ~.5
  • 40 Average Diameter ~ .59
  • .45 Average Diameter ~ .58

The total average difference is actually LESS than the difference between the hollowpoints pictured above. If you count expansions as being closer to a vital organ/artery (half the diameter.) then the difference is 0.060 with the picture vs a 0.045 spread with Lucky Gunner Average.  To put that in perspective, that’s less than 3/64 of an inch difference between the largest and smallest according to the Lucky Gunner average.

The individual bullet makes more difference than the cartridge.

9mm Hitting Ballistic Gel

Now look at this ballistic gel gif and how much everything is getting blown around.

Do you really think that tiny little size difference will matter that much?

I mean really?

In a certain sense it MUST matter because sometimes that TINY difference will occasionally allow you to hit something vital you would’ve otherwise missed….  assuming you shoot just as well with the larger caliber (and most people don’t).

I would give a TINY edge to larger calibers simply because their large diameter does occasionally make a difference.  But I would only give them A TINY edge.

Follow the logic:

  • If poking holes is about all pistol bullets can do.
  • And if 9mm, 40 S&W and 45 ACP all poke holes around the same size
  • then they should have about the same effectiveness. (with a very slight edge to the larger bullets)

Here’s the data to back up that logic:

An Alternative Look at Handgun Stopping Power.

I pulled some relevant data and compressed it to a single table:

 9mm40 S&W45 ACP
Average number of rounds until incapacitation2.452.362.08
% of people who were not incapacitated13%13%14%
Percent actually incapacitated by one shot (torso or head hit)47%52%51%

A few things to point out:

  • All of our cartridges took more than 2 shots on average to stop someone.  (though the 45 ACP was close to needing only 2.)
  • Their failure to stop rates were all within 1%.
  • Their one shot incapacitation rate was within 4%.

So if you compare the actual 9mm vs 40 S&W vs 45 ACP “stopping power” (incapacitation) numbers, it boils down to a measly 4%.  Like I said, I’d only give larger bullets a TINY edge.

It’s probably closer than that because of the effect being shot sometimes has on people.  Again from the same article:

In a certain (fairly high) percentage of shootings, people stop their aggressive actions after being hit with one round regardless of caliber or shot placement. These people are likely NOT physically incapacitated by the bullet. They just don’t want to be shot anymore and give up! Call it a psychological stop if you will. Any bullet or caliber combination will likely yield similar results in those cases.


So in most self defense scenarios, a 22LR  is just as effective for making bad guy give up as a 45 ACP.  I’m not recommending you carry a 22LR, but remember that almost any gun will do it most of the time….

I’d recommend 9mm as a minimum, because smaller bullets don’t really have the penetration and expansion 9mm has.  One or the other separately, but usually not both.  However, I’ve recommended a few people carry .22LR because they couldn’t hit the broad side of a barn with anything else.

EDIT: I recently wrote an article titled “How Many Rounds Do I Need For Concealed Carry?” I included a study about police officer hit rates and the FBI’s opinion on 9mm vs 40 and accuracy.  That resulted in some interesting numbers on how many rounds it takes from each cartridge to stop an attacker.  So 9 vs 40 vs 45, which do you think took the most rounds?   The answer might surprise you…


9mm vs 40 S&W vs 45 ACP Conclusion

I don’t really care which one you use as long as you are accurate with it.  They all poke around the same size hole and have around the same effectiveness.  Therefore, what matters is Where you poke that hole.

Hitting someone in the pinky finger with a .500 S&W Magnum is less effective than hitting the head with a 22 LR.  You’ll see me say this all the time: NOTHING trumps shot placement.

Nothing ever has, nothing ever will.

The famous western lawman Wyatt Earp was renowned for his skill as a gunfighter.  He has this to say about accuracy.

Fast is fine, But accuracy is final. You must learn to be slow in a hurry.

Wyatt Earp had gunfights with faster men many times, but he always came out on top.  Why? If you read more about him you’ll discover he always took time to properly align his sights before pulling the trigger.   Even at a distance of only 5-10 feet.

I found an interview with Wyatt Earp if you’d like to read his thoughts on gun fighting.  It’s well worth a read but spoiler alert: his theme is basically this:

NOTHING trumps shot placement.

I’ve said it before: you can’t miss fast enough to win a gunfight or fill a hunting tag.

That statement is borne out in my carry choice. I carry a 9mm for two reasons.  Reason #1 is because I shoot 9mm better than 40 S&W or 45 ACP.  Reason #2 is because 9mm ammo is cheaper than 40 S&W or 45 ACP, so I can practice more for the same money.

I would recommend you carry whichever you shoot the best.  It doesn’t matter to me if it’s 9mm, 40 S&W or 45 ACP.

What matters to me are rounds on target.

If you don’t have a pistol yet and/or are trying to decide what caliber to carry, I would recommend firing them all and then deciding which you shoot the best and are most comfortable with.  If you have gun loving buddies, you could ask to try their pistols out.  Failing that, rent some at a local range.

Fire them all, and pick the one you’ll shoot the best.  Remember, they all poke about the same size hole.  So pick the one you shoot the best or that you feel most comfortable with.  Again, I don’t really care about 9mm vs 40 S&W vs 45 ACP.

It doesn’t matter to me.

What DOES matter in a life and death situation is accuracy.

I carry a 9mm because I shoot it better than the 40 S&W or the 45 ACP.  Pick the cartridge you shoot the best, then spend a lot of time practicing.  That’s what will make the difference.

As an addendum, the FBI justification for going back to 9mm has this to say about the accuracy of various cartridges:

The majority of FBI shooters are both FASTER in shot strings fired and more ACCURATE with shooting a 9mm Luger vs shooting a .40 S&W (similar sized weapons)

And there’s one more thing….


How to “Cheat” the Normal Rules of Handgun Wound Ballistics

The winning formula for hunting or combat is this: Great accuracy + Great bullets = Win.   This section isn’t about cartridges, it’s about bullets.

I’m a firm believer that “If you find yourself in a fair fight, your tactics Suck“.

That’s why I don’t carry “fair” ammo.  And by fair ammo, I mean the same Jacketed hollow point bullets used by 95%+ of the people who carry concealed.

There’s better options these days.

The vast majority of handgun bullets can only poke holes.  But there’s a few extremely well designed bullets that can do more.  Sometimes a LOT more.

My current carry ammo is the 9mm Polycase ARX.  It was recently picked up by Ruger and is now usually sold as the Ruger ARX.  I intend on changing to the Lehigh Defense Extreme Defender (NOT the Extreme Penetrator) when my budget allows.

I won’t into the technical details, but they allow you create a MUCH larger wound that is possible with conventional hollowpoint bullets.  Additionally, since they don’t rely on expansion there’s no real possibility of them failing to do their job.

The Military Arms Channel did a great video on the Lehigh Extreme Defender’s performance.  The comparison was with the Federal HST.

So, my solution to the whole 9mm vs 40 S&W vs 45 ACP debate was to carry a 9mm because it’s what I shoot the best.  Then, I picked ammo that allows my 9mm to create a wound larger than a .45 ACP hollowpoint.

That’s what I call a win.

If you find yourself in a fair fight your tactics suck.  So don’t get caught in a fair fight.

I use “unfair” ammo, but NOT because I want to kill someone.  That’s the LAST thing I want to do.  I carry that ammo because IF I am ever attacked, I want to survive.  I pray the only time I ever draw my carry pistol is at the range to practice.  But if I’m forced to defend myself or others, I want the odds stacked in my favor.

So wherever you fall in the 9mm vs 40 S&W vs 45 ACP debate, remember one thing.  The winning formula isn’t using cartridge ABC or XYZ.  The winning formula is Great Accuracy + Great Bullets = Win.


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