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9mm vs. .40 Caliber - Sydney Vail (POLICE Magazine)

9mm vs. .40 Caliber - Weapons - POLICE Magazine
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9mm vs. .40 Caliber
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)
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 in uence many other law enforcement agencies to give the 9mm
jacketed hollow-point another look.
9mm vs. .40 Caliber - Weapons - POLICE Magazine
In the January 2013 issue of POLICE, I wrote an article titled "Stopping Power: Myths,
Legends, and Realities,"
(https://www.policemag.com/channel/weapons/articles/2013/01/stopping-powermyths-legends-and-realities.aspx) 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 e ectiveness 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 e ectiveness, 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 de ne the
concept of "stopping power."
I believe the de nition of stopping power for law enforcement should be a
particular ammunition's e ectiveness to render a person unable to o er resistance or
remain a threat to the o cer, 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 e ect. Obviously, shot placement is the only
realistic option for a law enforcement o cer.
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.
9mm vs. .40 Caliber - Weapons - POLICE Magazine
But handgun ammunition only has acceptable stopping power if the bullet hits a vital
structure that would "stop" the target from continuing the ght.
The Measurements
OK, let's return to our speci c discussion of 9mm and .40 S&W ammo and look at
some of the basic measurable di erences between these two calibers of handgun
.40 S&W
9.01mm (0.355 inches) 10.2mm (0.4 inches)
950-1,400 fps
900-1,449 fps
0.36-0.72 inches
0.4-0.76 inches
There is no debate that for a handgun round to be as e ective at incapacitating as
quickly as possible, it has to either hit the brain stem, injure a signi cant 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 signi cant enough loss of blood to make the blood
pressure go down to cause the brain not to work as e ciently, 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 di erence to account for a larger degree
of tissue injury; the di erence between non-expanded bullets is small as well.
9mm vs. .40 Caliber - Weapons - POLICE Magazine
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 a ected by stress, but the e ects 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 gun ght—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 o ers 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
9mm vs. .40 Caliber - Weapons - POLICE Magazine
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
The FBI report of an o cer-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 o cers attempting to handcu 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 signi cant 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 147grain Winchester jacketed hollow-point. Gel demonstrated a 12- to 14-inch depth of
penetration, and the autopsy ndings (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 scienti c
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."
9mm vs. .40 Caliber - Weapons - POLICE Magazine
The obvious aws 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
signi cant 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
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.
 Read more about
Ammunition (/tags?tag=Ammunition)
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9mm vs. .40 Caliber - Weapons - POLICE Magazine
Join the discussion...
1. Tom Ret January 23, 2016 @ 9:52 AM
Those you come on this forum and cry why the cops had to shoot the suspect so many
times should be pointed to the incident cited above. This is an example where one or two
rounds would not get the job done as this individual was shot 17 times with a 40 cal
handgun and an m4 and was still able to struggle before dying.
See all comments
9mm vs. .40 Caliber - Weapons - POLICE Magazine
9mm vs. .40 Caliber - Weapons - POLICE Magazine
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9mm vs. .40 Caliber - Weapons - POLICE Magazine
9mm vs. .40 Caliber - Weapons - POLICE Magazine
9mm vs. .40 Caliber - Weapons - POLICE Magazine
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