In the handgun forums and magazines, a new narrative holds that .45 and 9mm are virtually the same in “stopping power,” so we should all carry the 9mm for its (relatively) lighter recoil and larger cartridge capacity.  While lighter recoil and more ammo are certainly good reasons to go to a 9mm instead of something larger, are smaller bullets really as good as bigger bullets?

The answer, of course, is “it depends on the bullets.”  Historically, it takes superior bullet design and/or higher velocity for the smaller bullet to do as much damage as the larger. The smaller round is much more demanding of careful ammo selection, in my experience.  Any deer hunter will tell you that you have to carefully select .243 loads for quick, humane kills on deer, while there is a broader spectrum of .308 loads that will do the job.  Any soldier with a specialty in small arms will tell you that much more money and research has gone into making effective anti-personnel ammo in 5.56mm NATO than was ever needed for effective 7.62mm NATO.  In the same vein, while I’m usually perfectly comfortable carrying a 9mm for personal protection, I’ve found myself having to be MUCH more picky to find street proven ammo for that chambering than for my old favorite .45.

I’m not alone in that. A fellow writer, Charlie Petty, wrote 25 years ago in American Rifleman magazine  of FBI’s research at the time, “As the testing progressed, another factor became obvious. No 9mm loads came close to the 10 mm and .45. ‘We expected that there would be a gap,’ said (FBI’s Urey) Patrick, ‘but we didn’t expect it to be so large.’ In the first series of tests, the best a 9 mm could do was 67.5%. The .38 Spl. fared just as poorly, and the standard FBI-issue .38 Spl. (158-gr. lead hollow-point +P) also achieved a 67.5% success rate. Among the initial rounds tested, only the 10 -mm, .45 ACP and a single .357 Mag. round were able to score consistently above 90%.”

Time went on. Ammo got better, and the new designs probably benefitted the 9mm proportionally more than the bigger calibers, but all were made better. A famous wound ballistics specialist whose work was pivotal to the FBI’s testing protocols was Dr. Martin Fackler, who died last month. In a 2012 interview Dr. Fackler said, “The size of the hole the bullet makes, the .45 is bigger than a nine-mill. But how much bigger, by diameter, it really doesn’t give you the measure of how much tissue it disrupts.  What does is the area of a circle. Area of a circle, it was pi-r-squared. It’s the radius squared. So, if you take your .45, your point four-five-one and your nine-millimeter as your point three-five-five, take half, take the radius, square that, and what you’ll find is that the volume, or the area, of damaged tissue made by the .45 is about sixty percent more than made by the nine.”

Another recognized authority, Dick Fairburn, recently wrote in Police, “I will always carry the largest drill I can, so my choice for open/duty carry is either a .45 for social work or a full-power 10mm in the boondocks. When I need a small pistol for concealment, a 9mm with high-tech ammo will do.”

Bearing in mind that where the bullet strikes is probably more important than anything else, and there is a wide range of experience and ability to control rapid pistol fire, I’d be curious to hear what all y’all think about this.  Since this tends to be a very contentious topic on the gun related internet, I’ll remind everyone that informed opinion, experience, and facts are welcome here, and ad hominem argument is not.


  1. Whats more important then what caliber your carrying is how proficient you are with it. A head shot shuts everything down immediately leaving no chance of any reaction from the opposition. Go for the gold, practice makes perfect.

  2. The .45 acp is notorious for poor penetration. When using the 185 grain bullet it failed to penetrate deep enough to incapacitate a white tail deer at a range of only 15 yards.

    In 1945 the U.S. Military tested a .45 acp and it failed to penetrate a military helmet and bounced off of it at only 35 yards while the 9mm penetrated it at an astonishingly 125 yards.

    Many old time elephant hunters got themselves killed precisely because they were using big bore guns that failed to give adequate penetration while poor white farmers and professional game exterminators hired by the various British controlled Governments were issued worn out .303 British military rifles and succeeded in wiping out 95 per cent of Africa’s big game.

    W.D.M. Bell and Agnes Herbert used 6.5 mm rifles and Bell killed 1,000 elephants with it and Agnes Herbert said she found no difference in killing power between her .45 cal. elephant rifle and her 6.5 mm Mannlicher rifle.

    Moral of the story, its bullet penetration and bullet placement that kill not bullet diameter.

    People also tend to shoot smaller calibers more accurately as they tend to kick less, give less muzzle blast, are inherently more accurate and cause people to flinch less.

  3. A lot of good discussion on the topic. A key point is the target is variable. Size, health, on or off heavy illegal drugs, mental state all affect your ability to stop the threat. Initial stopping data was on non-current bullet technology. Current bullet technology is much better. Caliber choice varies on how far the threat must be encountered, close in city or distance desert area. The key point everyone agrees on is bullet placement. Chose the largest power caliber you can repeatedly fire accurately. As far as varied opinions on the web the more the better. You never learn something new if you just listen to yourself.

  4. Years ago I did a ballistic test on a stock 9mm commercial 115g JHP round and a reloaded 9mm r90 grain JHP round. The stock was a 115 grain JHP at 1150 f/s, the reload was a 90 grain JHP at an choreographed 1650 f/s. We used the block of clay vs ballistic geletan for comparison. Not exactly a good representation of human flesh, but it gave a comparison. The 115 grain gave a good wound channel which was classic and impressive. The 90 grain blew away the first 10 inches of the 12 inch block. No cavity was available to cast for comparison. This teaches us two things. One increased kinetic energy , assuming the bullet is not compromised by clothing or glass etc, increases performance. Two we must qualify any of these non-human tests as comparisons not actual performance in the field due to the variables human threats bring. The added benefit of the reloaded round was a flatter trajectory. Pressures were +P, and fed normally. Commercial ammunition now can achieve 2100 f/s in a 9mm bullet, cased in a 9×25.

  5. Mas, if i may use your nickname, you provide accurate info, for which i am grateful.

    .380 for casual carry, per reasons noted above; 1911 or 5-7 if possibility of serious work impends…

    y’all take care, sign up folks for the NRA!


  6. Why is a certain caliber needed for 300 pound feral hogs, but a lesser caliber is sufficient for a drug fueled 300 pound homosapien?

  7. talk to a trauma doctor and you will learn something specific,that is that effectively when lying on the operating table the doctors can only tell the difference between a rifle and a pistol and a shotgun wound, individual Caliber are impossible to determine.all things being equal bigger is better, however all things are not equal.a bigger bullet sacrifices capacity and often accuracy, it is a universal precepts of gun fighting that running out of ammo is a bad thing.functionally speaking any ammunition that will get 12 to 18 inches of penetration on calibrated FBI ballistic gelatin will work as a self defense short capacity is king so long as the bullet meets the minimum performance standards

  8. Mas….Practice, Practice, Practice.
    If you do not hit the target the caliber does not matter. If LEO’s miss 70-80% of the time….Practice as you may need to defend yourself. Largest caliber you can shoot comfortably and hit the 3X5 card consistently.

  9. Having not seen this before – the dialogue – I’m perplexed on one hand, and not at all surprised on the other: the latter usually having to do with personal experiences. Mr. Ayoob’s commentaries are always wonderful to ponder, and learn from. I have only this perspective: now retired, in my middle ’70s, blind in one eye—I have a keen sense of what ‘might’ be necessary for my survival, my wife’s, my children & grandchildren and the ‘stranger’ of St. Luke’s story. They too are our responsibilities if we have any means at all to help, even if unsuccessful. I carry (cross-draw kidney) a .40S&W Shield, Hornady Critical: to strange parts or known dangerous places I bring the extra-round mag along on the opposite side. Concealed, I’ve never been ‘printed,’ even by police or state troopers. It is well-concealed, even in a strange church, neither at my home parish. I doubt anyone even has thought about it.

    Ages ago, when absolutely critical, I carried a concealed single stack Nine—the where was Leningrad, in and out for thirteen years. Only in necessary desperation did I carry, however; and it wasn’t fun. I never had to call upon it; close on only one occasion. I don’t believe that calibre or velocity or what-have-you was very important. Most would likely agree.

    In al my years since those days, 1989 forward, I’ve had to call upon my Smith once, and did not have to discharge it. I did have to draw it. I think the most important piece here is attitude, and situational awareness. I have limited means, so practice badly distorts our budget, but I get out there when I can. I practice at home quite frequently – blind draw and point, snap caps some times, but always handle it, walk around with it, carry it like an old friend. That’s another missing piece for lots of people: their ‘choice’ doesn’t become friendly, like a favorite sweatshirt or a single-malt scotch. I think you have to love your piece, and count on it second only to your instincts.

    All these letters are really fun for me – I hope my personal experience helps some-one out there. Practice yes, know yourself—ABSOLUTELY.

  10. Mr. Ayoob, I respect you very much and you do some very good work. I went looking for more numbers to see what I could find about handgun effectiveness. This led me to The Truth About Guns. Link:

    To explain the data, there are four graphs. The first one shows calibers used in reported shootings. The second one shows the proportion of fights which ended with fatalities. The third one shows average rounds to incapacitation by caliber. The fourth one shows proportion of shootings where there was failure to stop.

    The first graph shows that 9×19 is overwhelmingly the most common round used, period. The next most common, 45ACP, doesn’t even have fully half of its representation. However, 45ACP, 40S&W, and 38SPC were all used a fairly similar number of times.

    The second graph shows how a percentage of often people died in shootings to different calibers. All the handgun calibers, all the way from 22LR to 44Magnum, perform fatally between 20-30% of the time. Only shotguns rated notably higher — >60% of the time. Of major centerfire handgun calibers, 38SPC, 380ACP, and 45ACP all more or less got exactly the same fatality rate of approximately 27%. 9×19 and 40S&W performed almost identically to each toher, but performed a tad below 45 and the 38’s. 357Magnum and 22LR were the only handgun rounds that scored above 30%, and both just barely.

    The third graph shows how many average rounds to incapacitation. Sorry, but the field data is not bearing out the research saying 357Magnum, 45ACP, and 10mm Auto scored one shot stops >90% of the time. Even the mighty shotgun’s numbers show that its one shot stop rate is only in the 80% range. The good news is that no caliber on average needed 3 shots or more to force a stop. 45ACP requires 2-3 rounds on average to force a stop. Same for 9×19 and 40S&W. Interestingly, most rounds took between 1-2 rounds to force stops, edging closer to requiring 2 more often than 1. Interestingly, 22LR and 32ACP come the closest to matching the shotgun’s numbers, being the only handgun calibers to stop with an average number of shots being closer to 1 than 2, but just barely. Even 357Magnum needs 2 shots more often than 1 to do the trick, and 44Magnum is tied with it.

    The fourth and final graph is where things get interesting. This failure to incapacitate graph changes the context of everything else. The smallest calibers: 22LR, 25ACP, and 32ACP, all had the highest rates of failure to incapacitate. The best performer of these, paradoxically, 22LR, failed to stop 30% of the time. The worst of this lot, 32ACP, failed to stop a full 40%, so nearly half the time. 25ACP fell exactly in the middle with a 25% failure rate. These rates were all much higher than for all other calibers. Interestingly, all other calibers, save one performed very similarly in this department. 38SPC and 380ACP did the worst of these, having failure rates of just over 15%. The rest, bar one, all failed between 10% and 15% of the time, typically hovering between 12% and 13%. 9×19, 40S&W, 45ACP, 44Magnum, and shotgun all performed about the same here. The one that beat all others? 357Magnum with a failure rate of just 90% one shot stop rate for 357Magnum is perhaps an exaggeration or used cherrypicked cases or cases otherwise chosen for unambiguity about the facts of the shooting wherein a one shot stop occurred, but it isn’t far from the truth.

    Now, is 45ACP the great manstopper as claimed? Not really, according to the data here. It doesn’t fare much worse than other pistol rounds of >300J muzzle energy. It’s pretty much tied with 9×19 and 40S&W. In fact, these latter two rounds actually slightly beat it out in percentages of failures to stop. I believe Wikipedia has a table showing various 45ACP cartridges and their one stop shot rates. If I remember correctly, the 45 which does this is some kind of JHP. According to my charts, however, both 45 and 9 work about 85% of the time. But if you’re referring to just pure kills, then both fall well behind the 357 and especially the shotgun.

    Do things like 38SPC and 9×19 fail a full third of the time as claimed by Mr. Ayoob? Not according to the data I’m looking at. Again, Mr. Ayoob’s data is probably procured from a study of shootings which involved just one shot or something else like that with an emphasis on finding one shot stops. This is not to invalidate Mr. Ayoob’s knowledge or opinions, which are some of the best-founded and kept current in the world, but an attempt to compare them to other extant science about shootings. I have to say, that science does seem to indicate that much of what he says is indeed plausible. It is entirely possible that improvements in projectiles and powders and practices have leveled the playing field. I don’t have the numbers with me to determine what the differences between current iterations of rounds are versus ones a decade or so back versus retro rounds versus their very first iterations. Doubtlessly modern powders burn better, modern bullets are better designed to fly better and hit harder, modern HP’s are not only far more prevalent and affordable than such bullets were in the past, but also expand much more reliably and fiercely. I would personally pin improvements in the performances of smaller rounds, especially within the last 30 years, more on improved fighting arts and training methods than on super deadly new technology, although improving tech has doubtlessly played a roll as evidenced by the current heyday of subcompact handguns in 9×19 and 380ACP using expanding bullet technologies that simply were not there not even 10 years ago. I think we’re seeing better performance from smaller calibers now, because people are being trained better how to fight, being trained to press the advantages of their weapons, and being better allowed to legally defend themselves at home and in public. Mr. Ayoob doubtlessly has played a major role in the teaching of Americans to defend themselves. Just 50 years ago, if someone could shoot at a round bullseye 45ft away and score 5/6 hits shooting a revolver one-handed, they would be considered good and trained. Now, however, people who get handgun training learn things like situational awareness, two-handed and offhand techniques, shooting on the move, aimed and point shooting (Jeff Cooper nearly made the latter a lost art), usage of cover, how to incorporate CQC into armed self-defense, and even basic tactics for different threats and situation. And the internet has made the proliferation of training materials greater than every before so that even someone buying their first defensive weapon can have some basic knowledge of what to do and how to do it, albeit at a much lower level of mastery than someone who does take actual professional instruction.

    It is problematic that it is extremely difficult to make an exact science of terminal ballistics. Phineas Gage survived having a steel railroad tie blasted right through his skull from jaw to crown in the 19’th century, but people die today by falling out of bed. And people in the 19’th century often died of minor wounds which got infected while people today can pretty reasonably expect to survive things like being shot in the torso, which was usually a death sentence in the past. People have been killed by .177 BB’s going through their eyes and into their brains while other people have lived through being shot through the middle by a 12.7×108 round. Terminal ballistics is far better at determining trends than solidly predicting exact outcomes, especially insofar as reactions are concerned. And then there are notes about various calibers we hardly see today. For example, Mr. Fairbarn was convinced that 7.63×25 (30Mauser) was a real slayer of a round and experiences of dealing with it and 7.62×25 would seem to bear that out. But try to sell modern Americans on a 30 cal high velocity pistol for fighting and they’d probably come up with a laundry list of reasons for why they think it wouldn’t work.


    1. Getting shot sucks.
    2. Having a gun is the most important things.
    3. Nothing kills like a shotgun.
    4. All handguns have fairly similar success rates and incapacitation times.
    5. Small handgun calibers have extremely high failure rates.
    6. 380ACP is the smallest caliber to reliably work
    7. 357Magnum is a beast among handguns.
    8. Most people survive being shot by handguns.
    9. 9×19, 40S&W, and 45ACP are all virtually identical statistically.
    10. it is more accurate to say small guns work the worst rather than big guns work the best.

  11. There sure are a lot of “beliefs” and “feelings” in the comments. Facts and physics don’t care about beliefs or feelings.

  12. I dont worry about caliber wars, i been thru em for years so now my definite carry gun is a .357 magnum LCR loaded with 158 gr XTP if 5 shots dont do the job , i dont know what else will!

  13. I used to hate 9mm.
    9mm has been shot way more world wide than 45ACP. More $ has been made by 9mm and more $ has been put into that round in the last 15 years to make it effective as used in current weaponry world wide.

    Surface area and the relationship to volume of wound has an inverse problem: rate of deceleration. If the 45 ACP was sped up a lot (more recoil then also) it could eclipse the 9mm for effectiveness. That’s not what the $ decided. The $ decided to re-create the 9mm. Now I like 9mm.

    Mabe next they can re-create the 10mm and make it outdo a .357 mag all day long now that the average shooter isn’t scared of recoil like everybody was back in the 90’s… wussies. 😉

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