9mm or .40 Caliber?

Editor’s note: The following article is from PoliceMag.com, and illustrates with great detail, why you would want to choose a 9mm over a .40 caliber.  As someone who has used a .40 for a long time (I also shoot many other calibers), it was an eye opener.  I can safely say that this article has help persuade me towards carrying a 9mm – because when your fear for your life, and .40 may not stop the threat.

After you’ve read the article, please feel free to leave your comments below.

9mm vs. .40 Caliber

The FBI’s decision to switch back to 9mm pistols and ammo is based on studies of wound ballistics and shooter performance.

January 22, 2016  |  by Sydney Vail, M.D.

 This man was shot with .40 S&W rounds to center mass, was not incapacitated at the scene, and survived the shooting. (Photo: Sydney Vail) This man was shot with .40 S&W rounds to center mass, was not incapacitated at the scene, and survived the shooting. (Photo: Sydney Vail)

At the end of October, the FBI announced that it was planning to swap out the .40 S&W pistols and ammunition now used by its agents and replace them with 9mm pistols and ammo. This was a widely discussed decision, given that the Bureau once partially blamed the performance of 9mm cartridges for the deaths of two agents in the 1986 Miami shootout and subsequently transitioned to 10mm and then to .40 caliber sidearms. This is also a widely followed decision because the FBI’s choice of duty pistol and ammo will likely influence many other law enforcement agencies to give the 9mm jacketed hollow-point another look.

In the January 2013 issue of POLICE, I wrote an article titled “Stopping Power: Myths, Legends, and Realities,” in which I discussed the wound ballistics performance of various popular pistol calibers as I have observed through my experience as a trauma surgeon and tactical medical specialist. My advice then and now is when it comes to claims about the effectiveness of handgun ammo, don’t believe the hype. Instead, look at the hard facts.

And now that the FBI’s decision to go back to 9mm pistols has ignited another round of debate about caliber effectiveness, it’s time to look at the real-world performance of 9mm and .40 S&W rounds in terms of wound ballistics.

Understanding Stopping Power

One of the least understood concepts in all wound ballistics is stopping power. So before we discuss the 9mm vs. .40 caliber in terms of wound ballistics, let’s define the concept of “stopping power.”

I believe the definition of stopping power for law enforcement should be a particular ammunition’s effectiveness to render a person unable to offer resistance or remain a threat to the officer, an intended victim, or self.

So how does ammunition accomplish this? You have two options. You can use a really large round at very high velocity like the 30mm cannon rounds from an Apache helicopter’s M230 Chain Gun, which produces substantial kinetic energy, or you can place your shot where it has the most effect. Obviously, shot placement is the only realistic option for a law enforcement officer.

A handgun bullet shot into the shirtless torso of a person causes a degree of injury due to the body absorbing the bullet’s energy and dispersing it in front of and around the path of the bullet. The projectile also tears through the tissue. This means that the kinetic energy of the bullet will create both a permanent cavity and to a much lesser extent a temporary cavity.

But handgun ammunition only has acceptable stopping power if the bullet hits a vital structure that would “stop” the target from continuing the fight.

The Measurements

OK, let’s return to our specific discussion of 9mm and .40 S&W ammo and look at some of the basic measurable differences between these two calibers of handgun rounds.

   9mm                               .40 S&W

Diameter             9.01mm (0.355 inches)  10.2mm (0.4 inches)

Velocity               950-1,400 fps                 900-1,449 fps

Expansion          0.36-0.72 inches             0.4-0.76 inches

There is no debate that for a handgun round to be as effective at incapacitating as quickly as possible, it has to either hit the brain stem, injure a significant amount of brain tissue, or cause extremely rapid exsanguination (hemorrhage). From a wound ballistics perspective, the diameter of the handgun bullet translates into the permanent cavity, the direct tissue impact or what is actually injured by the projectile as it passes through tissues. If there is a blood vessel that is injured, the larger the hole or injury relates to the volume of blood that is able to leave the vascular system in a period of time as to cause a significant enough loss of blood to make the blood pressure go down to cause the brain not to work as efficiently, then to cause the loss of coordination, which then causes the person to become a reduced threat and eventually lose consciousness…all over time.

In a head shot, the amount of brain tissue disrupted by a bullet produces varying degrees of incapacitation unless the brain stem is hit. So when comparing the 9mm to the .40 S&W, size is not a huge factor. If both expand to the maximum diameter based on bullet design, there is not a large enough difference to account for a larger degree of tissue injury; the difference between non-expanded bullets is small as well.

Penetration in living tissue is a guessing game for both of these rounds. Despite what many shooters believe, measuring penetration in ballistic gel—simulating muscle tissue—yields limited useful information about penetration in the human body, which is made up of more than just muscle.

There are too many variables to accurately predict what the actual depth of penetration will be inside a human body. I have found a wide variety of depths of penetration for both 9mm and .40 caliber rounds when operating or caring for gunshot patients.

More Rounds in the Mag

Our discussion now comes back to shot placement or wounding accuracy and the potential number of bullets required to increase or maximize the odds of injuring the body of a threat in such a way as to render that person incapacitated.

Shooting accuracy is affected by stress, but the effects of stress can be reduced through experience. To quote Bruce Siddle from “Sharpening the Warriors Edge,” “stress is a matter of perception and perceptions can be changed through the training process.” By training to deal with more stressful situations, and not training until you get it right but training so you don’t get it wrong, you have a much better chance of accurate hits under stressful conditions.

In other words, shot placement—which is critical to prevailing in a gunfight—must be maintained under the most stressful of circumstances. Having more rounds in your pistol’s magazine increases the potential for accurate shots. Hence the FBI chose to make the change to the 9mm round, which usually offers a higher round count per magazine, faster and more accurate follow-up shots, less perceived recoil, and very similar physical bullet characteristics to the .40 S&W.

From a trauma surgeon’s perspective, both the 9mm and the .40 caliber can wound, injure, incapacitate, or kill. However, shot placement is the best predictor of accomplishing the intended goals. I have treated patients with more than 20 “holes” in them that never caused enough tissue damage or bleeding to cause them to die. And I have treated patients with a single “hole” that did die. Remember, the discussion is the ability of a particular ammunition caliber with improved bullet characteristics to stop a threat, not living or dying but simply to temporarily or permanently incapacitate the threat.

The FBI report of an officer-involved shooting on Nov. 29, 2006, from a Pennsylvania police department makes for an interesting read on this topic. The assailant was shot in the chest and abdomen with 180-grain

.40 S&W modern hollow-point ammunition as well as .223 rounds from an M4. On autopsy it was discovered he had been shot 17 times with 11 rounds exiting his body. Despite these many wounds, he struggled with officers attempting to handcuff him before he died.

Limitations of Ballistic Gel

There are people who will read this article who will maintain that the early works of Dr. Martin Fackler were written in stone when in fact he provided a significant amount of quality wound ballistics data but kept an open mind, understanding the limitations of simulants such as ballistic gel. This is best represented in an editorial he wrote about an article published in the Journal of the International Wound Ballistics Association, Winter volume 1991;10-13, by E.J. Wolberg.

The article in question was an autopsy study by a medical examiner on “torso only” shots with a retained bullet, noting that patients were excluded if bone was hit or there was over penetration. This data was compared to gelatin data for the 9mm 147-grain Winchester jacketed hollow-point. Gel demonstrated a 12- to 14-inch depth of penetration, and the autopsy findings (with the bullet only passing through soft tissue) of a 10- to 17-inch penetration. The author’s conclusion: “Based on comparison of data from living tissue penetration by the 9mm 147-grain bullet with test shots of the same bullet into gelatin, it is concluded that gelatin can be a useful predictor of this bullet’s penetration and expansion characteristics in shots in the human torso.”

Dr. Fackler’s editorial comment to this statement and study: “What Gene Wolberg has done here is what every clear thinking LE agency should be doing. Skepticism and meaningful comparison are the essence of common sense and all scientific thought….Don’t believe that your tissue simulant is a good predictor just because some army lab or the FBI uses it and says so—check it out for yourself.”

The obvious flaws in this study related to a gel-to-autopsy comparison was that if a bullet hit bone, it would invalidate the gel comparison; gel is a soft tissue simulant only. Also excluded were the outcomes of all victims; did they live, die immediately, or die later?

So when the FBI decided to change from the .40 to 9mm, it was likely done with significant testing, evaluation, consideration of actual wounds with degrees of injury sustained, degree of training needed to maintain accuracy of shot placement, as well as many other factors not yet available to the public.

Think of yourself under a stressful set of conditions using a weapon platform and ammunition that maximized your skill set and training; limited your recoil and made for faster, more accurate follow-up shots; and gave you higher magazine capacity so that you could minimize the chances of needing to do a physical manipulation to perform a tactical reload in the attempts to stop a threat.

The facts are clear; not every bullet entering a body will stop a threat. Major bleeding takes time, and the time to incapacitation is unpredictable unless the brainstem is hit or the heart is destroyed, and even then the person has 10 to 15 seconds of life left. More injuries to more structures gives an improved potential of incapacitation, and when they are accurate shots, the results are more predicted to have the intended outcome.

Sydney Vail, M.D., FACS, is chief of the division of trauma surgery and surgical critical care and director of the tactical medicine program at the Maricopa Medical Center in Phoenix. He is also medical director of Tactical Trauma Immediate Response (Tac-TIR) Group, Cowtown, Peoria, AZ; director of the SWAT Tactical Medical Program for Arizona DPS; and a senior instructor for the International School of Tactical Medicine.

28 thoughts on “9mm or .40 Caliber?”

  1. Any bullet in a bad guy gives someone an advantage. .22 caliber bullets were (and still are) devastatingly effective with a head shot. Just ask the Mob hit guys. One of the biggest problems facing not only Police but also Military operations is drug fueled targets. Many of these drugged up perps are very hard to bring down. Our troops in the middle east found this to be an issue when insurgents would keep coming even after multiple "holes" were put in their terrorist targets. Shot placement is ideal but not always easy to do even with great training. Every scenario is different.

  2. Who else besides the FBI/LE uses 40S&SW? I know only a few non LE that fire that caliber. A big reason is cost. Could this be a ploy by the President to shrink the supply of 9mm? If the FBI and other LE’s start using 9mm then there will be a lot less for the general public to buy. High demand low supply equals higher prices. The President and his acolytes have stated that one way to bring about gun control is to make it too expensive.

    1. Even if the price went up 10 fold, it is still a great value, when you consider the circumstances of a round in use.

  3. As a trauma surgeon and county SWAT team member, I agree with carrying a 9 mm and changed over about a year ago. I can shoot more accurately, get back on target faster and have more rounds in the magazine. Ten years ago I was convinced by the available data that .40 was the best caliber for "stopping power". As a trauma surgeon, I can tell you that I can’t tell the difference between the calibers based on the tissue damage. They both simply put holes in structures. What matters is where that hole is rather than the size of the hole. A high powered rifle is a different story. Thanks for the article!

  4. .40 is better and punching holes through thick materials (Carhartt Jacket, or a bear).

    Works just fine on soft targets too. Bang!

  5. As a CCW holder I can not carry enough ammo to spray and pray. I pray everyday that I get enough practice in to ensure my 6 rounds of .45 have enough stopping power.

  6. I’m starting to shop for my first pistol, so this is very timely, thanks! Great info, the article and some of the current comments have been very helpful.

  7. I carry a 9mm, but I also own a 40. The local LE range is full of 40 brass free for the taking. I reload so that helps with costs. Plus when 9mm ammo supply dried up 40 was back on the shelf quicker. I can buy a conversion barrel for my Glock 22 to shoot 9mm or 357 sig. That makes it a good choice for preppers. Also the military must shoot FMJ so that would be why the terrorist are full of holes and not stopped. If FBI/LE transition to 9mm like most other global police that may cause production to go up and eventually bring down costs after the transition ripples are over.

  8. We are taught in PHTLS (Per-Hospital Trauma Life Support) that 80% of our patients live from hand gun shootings. I had a patient dead on my arrival to scene with 7 bullets holes from a .22 – we were told per PD. I had a lady shot in the chest from a 9mm or .38 by her husband – it went through the breast and into her bicep. It never entered her chest cavity. Then the husband went into the other room and shot his self in the head…1144. I have used .45 1911 since I was in the Navy; I am so familiar with the 1911 from military to civilian that it is hard to think about changing, but now with my wife I am considering a 9mm just for easiest of shooting and availability of rounds. I think I still want a 1911.

    Does any know if they compared 9mm with .45?

  9. Go with .45 ACP. Our military has used 9mm through countless engagements since 1985 and is switching back to .45 for a reason. It might not be new and exciting, but it’s tried and true. Even though the round count is less, the stopping power is greater. I’d rather have one well placed shot stop the threat than try to squeeze off two or three shots accurately, to accomplish the same goal.

    1. The military argument doesn’t fully apply to the police and civilian market because the military is using ball ammo.

  10. I like Iceman’s comment that "Any bullet in a bad guy gives someone an advantage."

    I’ve read of many examples where amazingly someone ISN’T stopped immediately by shots that should have put them down. Drugs, adrenalin and who knows what else effect the situation.

    I’m consistently reminded that the best chance I have of stopping someone is with the gun I shoot best and/or can most easily access. A 40 cal is attached to the underside of my desk and I can shoot it well in that situation. No way could I use it effectively out and about because there’s no way I could have it easily accessible and it’s heavy enough for me not to use it as well in outside situations.

  11. Having fired both 9mm rounds and .45 rounds, and as a now retired LEO and Firearms Instructor, I see the question of "which is better" to be not a black or white issue. Of the two, I’ve mentioned, I prefer the .45 ACP. But, it’s basically whatever round you, as the shooter, have the most confidence in and are the most proficient with.

  12. I think the .40 does not provide enough stopping power (view the photo in the story.). I think the 9mm is even less effective (witness Gabby Gifford – shot thru the brain w/ a 9 and still walking and talking). Give me a .45acp but I think a .50 cal may be even better. The number of rounds in the mag is not nearly as important as the placement……..Thomas L

  13. If shot placement is the "correct" answer, wouldn’t .45 or .40 placed equally well be "better"? Train to the mission. I.e. better training should result in better shot placement. That being the case, why not simply train better with larger caliber?

  14. Quote "So when the FBI decided to change from the .40 to 9mm, it was likely done with significant testing, evaluation, consideration of actual wounds with degrees of injury sustained, degree of training needed to maintain accuracy of shot placement, as well as many other factors not yet available to the public."
    So this author can recommend whatever they want, but with the "likely" term used, they really don’t have a clue WHY the FBI is changing back to the 9mm. I could just as easily say it’s "likely" that the limp wristed metrosexual male and female agents (politically left leaning and anti-gun) now being recruited for their advanced degrees in underwater basket-weaving and social engineering are just not up to firing a .40 caliber handgun because it has a little more recoil than a 9mm. Seems to me they had the same problem with the 10mm handgun and sub-gun. Shot placement is still paramount, but it still comes down to the fact that a handgun is only there to provide me an opportunity to fight back to my long gun. I have been shooting my .40’s for years & love them, also have a few 9mms. But either is just a tool. I don’t suppose minimal training and exposure to re-qualifying once a year could be changed to quarterly to make sure all are proficient? Remedial training? Make it fun to give them more exposure to a tool that, when used, should be an extension of themselves not some unknown glob of steel/aluminum/plastic on the end of their arms.

  15. Almost every comment goes off topic. The comparison here is 9mm to .40 cal.
    Not .45 ACP, .22 cal or .50 cal hand-cannons.

    That said, I once owned an Astra .40 cal, and while I liked the gun due to it’s balance and how it fit my hand, I found it to be a bit much for me in the way of recoil. Certainly I could have shopped around and found something of the same caliber with less recoil, but once moving to a 9mm, I discovered this was just a better fit for me. This taught me that a person’s choice of firearm should, among other considerations, be made according to what is the best fit for you personally. One should consider their own stature, the size and strength of their hands, and what just feels better for them. This, I truly believe increases your odds of neutralizing a threat with greater efficiency. The only caveat I would add to this is that within those considerations, it would be foolish to think you can defend yourself effectively with a small caliber weapon just because it has less recoil and is easier to hold in your hand. Stopping power is the name of the game. You have to neutralize the threat as quickly and as effectively as possible to prevent a lengthy encounter, thus reducing the chance of further injury to yourself or others.

    Within law enforcement, there are obviously Department issue standards and so, officers and agents are expected to meet those standards and carry what is within those parameters. For we civilians, I would recommend using the caliber, make and model of firearm that is optimally suited for your personal body characteristics.

  16. John Doe’s post is on point. Mandated female participation leads to females failing to qualify with harder-kicking rounds. Further, more and more men are being raised by single mothers so are apt to develop female-inspired prejudices against shooting. Meanwhile, Thomas L almost hit the mark when noting Gabby Giffords survived a 9 mm headshot–given how little mental horsepower she had, it’s likely the bullet sailed through empty space.

    1. The one that is reliable (min 100 rounds without a jam or malfunction) and fits your hand well. Rent a few from a local range.

  17. When I was learning to shoot as a kid I was taught to shoot it, not shoot at it. So I agree shot placement is critical. Part of shot placement is a gun that fits your hand. My Ruger 357 fits my hand, but the S&W does not. So I can qualify with the Ruger but not with the S&W.

  18. The answer to the question of 9mm vs. .40 does not lie in the diameter of the bullet or in shot placement. While a critical element shot placement becomes an elusive matter when the defender is under stress and being shot at. Modern technology and physics becomes a key point in this debate. With the advent of modern bonded hollow point ammunition, the round finally does what it is designed to do, that is stay together, expand and provide significant depth of penetration. The other factor is simple physics. Being a former law enforcement firearms instructor and having carried either a .40 or a .45 all of my career (except for some 9mm time over seas) I must relinquish to the fact that you can recover from recoil faster with a 9mm than you can a .40, this means more rounds on target. It takes an average of 2.3 rounds to put someone down, so if i can deliver those rounds faster it gives me the advantage. Even though I still do not own a 9mm I must give it the win on this.

  19. One factor of shot placement and incapacitation not covered in this article is the result of a shot to the pelvic/hip bone. I would be very interested to hear some clinical data concerning the 9mm and .40 S&W respective ability to shatter a grown man’s pelvis and thus stop the threat. Massad Ayoob has spoken of this very scenario, stating that for this reason it is not advisable to carry a caliber smaller than a 9mm, indicating that a hip shot will shatter the hip bone and stop a charging assailant from taking another step. Furthermore, the adult pelvic bone is not a small target, like the brainstem. Another interesting point is that most body armor stops short of covering this region of the torso (the bad guys use it too). I, for one train with, and would most definitely employ this tactic, if faced by a charging assailant with a blunt or edged weapon. And if incapacitation involves removing their ability to stand upright and use their legs, I would most certainly share the love with stationary targets. This may not be the best first point of aim in many scenarios, but in training and in a crucial confrontation, it should not be overlooked.

  20. If you have proper shot placement, all things being equal, a heavier bullett will do more physical damage than a lighter bullet: .45 is better than .40, which is better than 9mm, which is better then .380, etc. I other words, hit someone with a bowling ball, softball, baseball, and golfball, and what are the end results? Heavier generally does more damage, (not to get into baseball/softball arguements).
    What about bullet design? How does that factor into the article above? Just as gelatin tests are void v. human body, because we are taught to shoot at center mass, whuich is bone armour, not soft tissue, the above information is also not valid since we do not know what types of projectiles are being commented on.
    Three previous valid points:
    1) 9mm kicks less, and holds more, however, I submit that you REQUIRE more rounds to put down an assailant.
    2) 40 cal is hardly larger than 9mm, however it weighs considerably more, therefor it does more damage, albeit with more recoil.
    3) Pelvic shots not only destroy a persons ability to stand upright, it also is more likely to rupure a majour artery and cause the assailant to bleed out faster, regardless of what type of drug the "perp" is on, he/she will expire faster.
    For all of that I will still choose either a .45 ACP or a .38 Spl as my primary defensive round due to a heavier bullet and more stopping power. I am on target out to 25 yards with my Gov’t model, which means I can hit someone anywhere from 7 to 10 feet out to 25 yards if necessary.
    I also advocate for using teh pelvis as the PRIMARY aiming point, since recoil raises the muzzle, so the following rounds- traveling upwards on target- will destroy the opponents ability to respond.
    I pitty the person who only trains at living-room distances, because the one time someone shoots at them from further away and they will not be capable of returning fire due to the distance.
    For anyone who says it "kicks too hard", I am 5’5", and I shoot a single shot .44 Mag with 320 grain bullets, and that is completely controlable out to 200 yards, all day long.

  21. Phillip Kirkland

    Great article. I carried a Sig 40 for several years and because of the size, capacity, weight and kick, I decided to go with the Ruger 9 and I love it for all of the same reasons. Although Sig, out of the box is incredible and accurate, I have done almost as well with the Ruger, by working on sight adjustment, trigger pull /squeeze


  22. @Badger Jack – While you argument of a "heavier and larger bullet will do more damage" is technically true, the reality of it is very minimal.

    Slow-mo videos of a "wound cavity" in ballistic gel might look cool, but it really is doing no permanent damage. At the speeds of handgun rounds, the only permanent wounding mechanism is the crush damage (the cylinder of material displaced by the actual bullet). So in your point a .45 will make a slightly bigger hole than a .40 and so on.

    However, the slower, larger, heavier rounds will be stopped easier than the faster, smaller, heavier rounds because of the additional surface area of damage they are doing. In practical terms, that means they will all stop in about the same distance (12-18") in "soft human tissue" all other factors the same.

    That leaves us with only a few factors left. Primary wound cavity (the crushed tissue in the cylinder of damage), round capacity in a given firearm size, and subsequent shot placement (from recoil recovery).

    Given enough practice, the shot placement factor is practically even between all major calibers (but you have to practice a lot and .45 is more expensive than .40 which is more expensive than 9mm and so on).

    So now we are down to the two factors of hole size and round capacity. There can’t be any argument that the smaller hole producing rounds will allow you to carry more in the magazine so it becomes a balancing factor between the two.

    For hole size to matter, you would have to have just missed a major organ/vessel (we’re talking millimeters) where the larger round would have just had enough area to hit it. Under stress millimeters don’t factor so it comes down to luck (with a slight edge to the larger rounds). Some studies have found that there is little difference in total rounds required to stop an attack (and the slight increase as the caliber gets smaller has been attributed to faster follow up shots before the attacker was realized to have stopped).

    Having said all of that (and assuming you practice a lot, which some people won’t), it comes down to your decision to have a little more luck vs having more rounds to work with. I don’t think there is a right answer for everyone and there definitely isn’t a "perfect round". It’s a decision that you have to make for yourself.

Comments are closed.

Help Us Spread the Word