The Return of the 9mm (Part Two: The 9mm Awakens)

The Hornady XTP bullet seen here performs fairly well in ballistic testing, though the newest designs such as the Ranger SXT from Winchester is among the best performing defensive handgun ammunition around.

The Hornady XTP bullet seen here performs fairly well in ballistic testing, though the newest designs such as the Ranger SXT from Winchester is among the best performing defensive handgun ammunition around.

Last week, I wrote about the nine-millimeter’s return to law enforcement agencies, including the FBI, who had shunned the performance of that round nearly two decades ago. While perusing some of the comments and emails I received in response, I found a link to an excellent article in POLICE Magazine titled 9mm vs. 40 Caliber. While I don’t enjoy the typical pistol caliber debate, as you can find these ad nauseum on any Internet gun forum, the article goes in depth into wounding mechanisms and the mechanism of “stopping power”. Also of note is that the article was authored by a trauma surgeon. Here are my takeaways from the piece.

The Math of Stopping Power

Modern defensive handgun rounds wound by creating a wound channel, which is measured in width of the channel and penetration. Handguns bullets do not produce a temporary cavity that damages tissue to a significant degree (unlike rifle rounds) because they do not carry enough energy to do so. Therefore, the permanent cavity is caused but the bullet expanding and then tunneling through tissue. The difference in expanded (or unexpanded) diameter of 9mm and 40 caliber (or even 45 caliber) is very small and insignificant to account for a difference in injury to tissue. As for penetration, this is a guessing game in live tissue, and even more so through barriers. I am satisfied with the FBI’s protocol of 12-inches of penetration through calibrated ballistic gelatin (though there are limitations to these results as well.)

Capacity and Other Considerations

Shot placement is key, and the additional capacity of a 9mm magazine over a 40 caliber (or 45 ACP) one in a service pistol certainly increases the odds for us. Decreased shot to shot times and less recoil (as I mentioned in last week’s article) also helps us out.

Ballistic gelatin testing gives us a way to compare bullet performance in a standardized way, but there are too many variables to predict performance in the real world, so the author admonishes us to use common sense. I agree.


The point of the article was that both 9mm and 40 caliber perform fairly similarly from a perspective of wounding potential, based on the author’s experience in the operating room. But given the advantages of 9mm: lighter recoil, easier to control, higher capacity, etc., help the shooter improve shot placement which is a greater determining factor than any difference in terminal ballistics.

Read the POLICE Magazine article here.


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About Tim Lau

Tim Lau has over a decade of experience as an end user, armorer and instructor. He has worked for several well known firearms training organizations, and holds multiple firearms instructor certifications. He owns and operates 10-8 Consulting, LLC, which provides industry consulting services as well as marksmanship and specialized firearms training to qualified civilian, law enforcement and military personnel.

10 thoughts on “The Return of the 9mm (Part Two: The 9mm Awakens)

  1. Good pair of articles.
    We tend to get wrapped around caliber when what we should be concerned about is whether a handgun fits or not. Recoil is part of fit. I have never been a big fan of the .40 but I have little experience.with it. For me (and just me) I find the .45ACP works the best especially when fired out of a full sized revolver with a good grip.
    Just my two cents.

  2. I agree, two very good posts–in the end it’s all about bullet placement, as it always has been (which is why I transitioned for the .40 to the 9mm three years ago).

  3. Perhaps. And perhaps gelatin replicates the non-homogenous nature of live mammals wearing clothes, running, kicking, and fighting.
    But the natural mechanic in me has a hard time thinking that a bullet that’s twice the cross-section size and twice the weight going only a little bit slower won’t be able to reliably break more stuff than the little bullet.
    And if the little bullet is just as good, why aren’t we all clamoring for the .32 ACP, which offers big advantages over the mean ol’ 9×19 in terms of capacity, recoil, and blast?
    Why not the .25 ACP? Or is there a line somewhere where size matters?

    • Note the lucky gunner test:

      If one is to say 9mm is adequate, that is fair. To say that 9mm, 40 and 45 perform close to the same, that is highly debatable. There are substantial differences at least in ballistic tests. Some people now actually believe a full house 357 magnum performs the same as a +p 9mm. The same people would never consider the 556 and 308 to perform the same. If we rely on ballistic’s testing then we should rely on it, not just choose what we want to believe.

      Also when it comes to recoil, the vast majority of people’s experience with 45ACP recoil is on larger guns than the 40 handguns for instance Glock 22 and 21. That shouldn’t be ignored.

      You would think I shoot 40 all the time. I don’t. I shoot 9mm most of the time but the reason isn’t recoil or pressure (they’re the same pressure). The reason is ammo cost and because I believe the 9mm is adequate. I don’t believe it performs as well as 40 or 45 and for sure not in hardball which a ton of inexperienced people use at home.

      • You linked a test which only shoots through denim layers and did not test any other barriers. Their testing did not focus at all on consistency of performance either. If a round averaged 12.5″, what was the standard deviation and how many of those shots were less than 12″? Consistency of performance is just as important as the average performance, because one of those “less than 12″ shots” could be the one you connect with in a gun fight that fails to stop an attacker.

        I’ve seen the FBI ballistic data. The 9mm rounds they are using today are superior to any .40 or .45 round on the market in both average penetration and standard deviation of penetration and expansion, while only giving up a few hundredths of an inch in diameter. The 9mm rounds get through hard barriers easier and perform the most consistently when they hit soft tissue on the other side.

    • This is unsubstantiated by i think it’s the circumference, not the sectional area of a bullet that matters. It’s the tissue that’s left that is bleeding and bleeding comes from the surface left after the meat has been crushed.

  4. When it comes to self-defense encounters, we must have more tactics than just stand there and pull a trigger. Cover, concealment, movement all provide an added level of success to the one whom uses it effectively. As for mechanical wounding of the pistol cartridges, I don’t think there is enough of a difference to enhance or change my tactics. Capacity helps stay in the fight longer. Recoil impulse impacts accuracy, well placed shots and how easy you can manipulate the weapon. Not every shot will replicate what you encounter on a static gun range. I think bullet construction is more important than diameter of said bullet.

  5. I have seen an informal penetration test with a 9mm, 40, and 45 ACP on a frying pan at about 10 yards. The 9mm and 40 went thru. Although it left a hell of a dent, the 45 ACP did not. I was a little surprised by this, but not shocked. I have always been a fan of the 45 and will continue to be. I have also owned plenty of 40’s too. I do own more 9mm’s than anything else at this point. They all have their highlights and could be debated all day. I have never been attacked by a frying pan or anyone made of ballistics gel and more than likely won’t be. I must say Chris Costa said it best “Don’t put your faith in one particular caliber, it will let you down. Put your faith in your skill set.” Those are words to LIVE by.. Just my opinion. Keep training!

  6. Forgot to mention, my vote is for 9mm. It took a few years for me to realize this. Many of the top trainers world wide endorse it as well.

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