This is a debate as old as the interwebs, and not likely one that’s going to see a firm ‘law of ballistics’ set in stone anytime soon. For the time being, the consensus from the experts is this: the 9mm Luger, in a bonded, jacketed hollow-point, is nearly the ‘ideal’ defensive round due to high capacity magazines, low recoil, reduced muzzle flip, cost per round for training, and reliability of use.
But why this round? Why the 9mm in a semiauto, versus the authoritative 10mm or the iconic .357 magnum? Here’s some history, for the interested; it covers a complex history of personal carry, military issue, and small arms development at the local and global scales.
At the turn of the 20th century, the .32 S&W (and variants) was popular for personal defense, mostly because it was a small round that was ideally suited for very small, discreet pocket revolvers. Rounds like the .25 ACP and even the petite .22 Short stayed in vogue for a long time, loaded in so-called ‘pocket guns’. A contributing factor was metallurgy and gun design; only large, thick-walled and heavy-barreled pistols could safely handle the high pressures of heavier loadings. The .380 ACP was among the most powerful rounds available, chambered in the Walther PP series and the Colt M1903. Few people outside the military and law-enforcement had cause to carry a full-sized ‘combat’ revolver.
The .38 Special was developed in the early 1900s to replace the woefully anemic .38 S&W, disparaged by the US Army for poor performance against Moro tribes in the Philippine-American wars. The wheels of the military tend to turn slowly; in 1909, the US Army instead adopted an improved version of their stoutly reliable .45 Long Colt round in the M1909 New Service revolver. This was a stopgap measure while the military investigated procuring an entirely new service pistol; one of the chief requirements for their new service pistol would be a .451″ round matching the M1909’s performance. While the Army demurred on adopting the .38 Special as their primary service cartridge, it did make a splash among civilians and police.
The platform for this new round, the original M&P Revolver (later the Model 10), became extremely popular among US police authorities, particularly when various high-mass and high-velocity loads were developed for it. A .355″, 200 grain bullet loaded to nearly 700 fps proved to have good wounding effect, in some cases even tumbling on impact to inflict gaping wound paths. During the ’30s, early body armor and steel-plated auto doors were in vogue among gangsters; it was found that the much faster .357 magnum, built by legendary cartridge developer Elmer Keith, was far more capable of penetrating these barriers than other handgun offerings available to the police. Switching from .38 to .357 was logistically extremely simple for a large number of reasons; particularly with the ability to practice on the range with .38 Special and then load .357 for patrol without having to change guns!
The M1911A1 was adopted by the US Army in 1911 to replace the M1909 series of revolvers. The combination of a semiautomatic pistol with a 7+1 capacity and the superior wounding potential of the .45 ACP proved to be a decisive improvement over the old .38 S&W, and was popular among GIs in WWII and beyond. Domestically, the .357 reigned supreme stateside for decades as the preferred round among law enforcement officers, being an exceptionally flat-shooting round with unbeatable penetration, and loaded with blunt wadcutter rounds could do tremendous damage to a target.
The argument has gone for years (and not necessarily wrongly) that the .45 ACP was a ‘better’ round than 9mm and .38 Special. But what killed the .45 wasn’t so much the round as the ergonomics– the only revolver chambered in .45 ACP at the time was the M1917, which is roughly equivalent to a modern N-frame revolver in terms of size. The cumbersome M1917 also required fiddly, tedious moonclips or specialized .45 Auto Rim ammunition, making it far less appealing than a Model 10 revolver.
There were many other contributing factors that lead to the revolver’s dominance over semi-autos; ease of concealment, reliability, and simplicity of operation were chief among these. Admittedly, reliability among early semi-autos was less than ideal. Additionally, the smaller cross-section of a .357 magnum round (.355″ versus .451″) meant that it had better performance against early body armor and barriers such as auto doors and glass, making them popular among cops. Where the .45 ACP and 9mm are copper-jacketed, the .357 could be loaded with soft, expanding lead. As the predominant competitive dynamic was bullseye target marksmanship, there was little incentive to develop a semiautomatic pistol into a service and carry weapon. Accurizing a revolver was cheaper and easier than doing the same with a 1911 or other semi-automatics on the market.
From a practical perspective, few police departments wanted to invest the time and money in equipping their troopers with department-issued semiautomatic; beyond buying all the firearms, there are significant expenses involved in training, equipping the armory, maintaining the weapons, and changing ammunition reserves.
And, chiefly; the .357 had a solid and well-earned reputation as a decisively effective manstopper in a gunfight. The 9mm Luger FMJ, in any platform, simply could not compete; and the M1911, while a fantastic pistol, is a firearm that demands a firm grip and a great deal of dedication from the shooter behind the trigger, as well as careful maintenance. It would be most of half a century after WWII before the police would take a serious look at switching en masse to a semi-automatic service pistol.
It wasn’t until the advent of IPSC style shooting that people started paying very serious attention to what Jeff Cooper, Bill Wilson, and the men at the original Gunsite training camp were doing; the training games they were playing tossed conventional bullseye marksmanship out the window in favor of terms like ‘acceptable accuracy’, and turned the shooting world on its head by examining pistols as a serious combat tool with a surprisingly robust scientific methodology. And overwhelmingly, they preferred the M1911, the nearly-as-antique Browning 9mm, and even the newfangled Czech-made CZ-75. With modern advancements in metallurgy and gunsmithing making semiautos much more reliable, and the utility of higher-capacity magazines, that brought back around the age-old question: which caliber is ‘best’?
All things being equal, a .45 ACP and 9mm Luger in FMJ can completely perforate a human target, but the .45 will do so while creating more cavitation. Penetration is more important than cavitation, but only inasmuch as say, torque might be more important than horsepower. The FBI has stated that their minimum standards for penetration is 12″-18″ in calibrated ballistics gelatin; anything below that is not sufficient, and beyond that is just overpowered. After meeting the standards for penetration and shot placement, cavitation is a key factor in determining a bullet’s effectiveness in tissue. Remember, there are only four ways to stop an attacker; shock, pain, exsanguination, and incapacitation. A larger bullet displaces more tissue, causes a larger wound tract, and is less deflected by bone or variations in tissue density. The only alternative to a larger bullet is to push a smaller one up to extreme velocities– hence, the .357 magnum round.
When the first hollow-points were released by a company called Super-Vel in the late 60s, many manufacturers sat up and started paying attention to the radically increased wound capability. Though ‘mushrooming’ bullets were banned by the Geneva convention, there was no such restriction for their use among law-enforcement personnel and civilians. Super-Vel had taken the concept of a ‘dum dum’ round, designed to expand or tumble on impact, and refined it into a hollowpoint that would consistently and reliably open up into a much more effective wound channel.
Research into the idea of expanding bullets created a flood of new possibilities for firearms– pistol rounds could be engineered to expand well over their normal diameter, muchly obviating the need for ‘big bore’ or high-velocity rounds in self defense.
With the invention of the modern hollowpoints and improvements in gun design, the utility and reliability of the .38 Special in a revolver was no longer a decisive advantage over a modern double-stack semi-auto pistol. The US Military had already adopted the very well-proven M9 Beretta in 1985, with a whopping average of 22,500 rounds between stoppages. Domestically, the FBI led the way in formally adopting a double-stack semiautomatic pistol after the notorious 1986 Miami Shootout.
The FBI determined that not only were wheelguns in .38 Special likely not effective enough for ‘serious’ use, but they also lacked sufficient capacity for a prolonged engagement. At least one agent was too badly injured to be able to reload his six-shot revolver during that shootout. Moreover, the FBI concluded that their 9mm Luger rounds (an early 115gr Winchester Silvertip) lacked adequate penetration, as one such round stopped a fraction of an inch from the heart of one of the shooters.
It was found that the #1 factor behind guaranteeing consistent expansion in a target is a function of mass and velocity. In short, a heavier, faster bullet faces more inertial resistance, which causes the round to open up. By the same token, a lightweight hollowpoint tends to lose penetration as its surface area expands, making hollowpoints less optimal in lighter bullets (such as .38 Special and .380 ACP). One of the most useful metrics the FBI employed after the shootout was the use of ballistic gelatin, which roughly approximates human tissue and provides a very consistent replica of the effect of a bullet in the human body, for comparing the performance of widely disparate bullet designs.
Jeff Cooper, working with Norma Ammunition and a company called Dorneus & Dixon, developed the 10mm Auto round– a .400″ bullet in a 1″ case, flinging a bullet as heavy as the .45 ACP, but doing so at a brisk 1100+ fps. It fulfilled all the FBI requirements for their new test in calibrated ballistics gelatin, expanding aggressively in diameter and penetrating through denim, automotive glass, and even steel barriers. It was, if anything, too aggressive; FBI agents found their marksmanship scores going down rather abruptly and many agents complained they couldn’t shoot as accurately or efficiently with the larger-framed guns and the harsher recoil of this hot new ammo. After downloading the 10mm to more manageable levels, the FBI worked with Smith & Wesson to develop the .40 S&W in 1990; before the year was out, Glock had modified their extremely successful Glock 17/19 frame to fire a .40 S&W round, several weeks ahead of the release of S&W’s Model 4006. For most of 20 years, the .40 S&W would sit atop the pack as the ‘best’ option for a combat pistol, neatly straddling the divide between .45 and 9mm.
The status quo has been for many years, the following: ‘serious’ shooters use a 1911 in .45, cops run .40 S&W, and civilians use 9mm compact pistols. But in the last five to ten years, the lines have blurred, particularly as the internet’s exploded into providing cross-pollination between competitive shooters, professional gun owners, and the huge buying body that is the civilian market. With ever-increasing amounts of data on the internet and research methodologies constantly improving, all three facets of the gun world can contribute to the sum body of knowledge. This is why compensators and red dots are becoming more common on combat pistols; why the military is adopting modern shooting methodologies and techniques; and how civilian demand for exceptional handguns is pushing the market into ever-broadening innovations and creations faster than the military can keep up.
Though it might change again soon, the consensus among the end-users at large is that 9mm JHPs now perform nearly as well as .40 S&W or .45 ACP in gunfights. Coroners have asserted that they have a difficult time discerning the difference between the three rounds without the use of calipers, and as we introduce better metrics for performance– the use of shot timers and scoring targets– we can say definitively that while a .45 ACP might have more expansion (+ .2″-.3″ at most) than a 9mm does , on average, a shooter is going to be more effective with the higher capacity and lower energy of a 9mm round, without losing meaningful ground in terms of effective lethality.
Lucky Gunner has one of the best, most singly comprehensive comparisons of side-by-side rounds that I’ve ever seen, here. It’s worth perusing as a very serious, rigorously scientific comparison of the various loads out there. This is a good baseline for gauging how your round will perform in gelatin, but it is not a substitute for range training or getting your own hands on your ammo and doing your own evaluations for performance, accuracy, and reliability. And no matter how well a round performs in ballistics gelatin, that is not a substitute for real world testimony, and it is not a correction for a lack of fundamental shooting skill. 3 badly placed rounds of .45 HST +p and 5 misses do not equate two excellently placed 9mm bullets. Bear that in mind when you start salivating over the datasets– power’s good, and speed is fine, but accuracy’s final.
In short, running .45 or 10mm or .44 might make your bullets more effective, but the tradeoff is that you are going to be a less effective combatant in a gunfight. A requisite for winning a gun battle is maximizing probabilities; the probability that you will hit the target accurately and quickly, and that the bullet will do sufficient damage to end the engagement. The 9mm sits at the ideal point between those two lines on a graph, at the cross section of ‘maximum efficiency of the shooter’ and ‘maximum effectiveness of the rounds available’. Don’t fall prey to the most dangerous of shortcuts: trying to ‘buy’ your way to a better level of competency on the range.
Additional resources used: http://www.pointshooting.com/1a10mm.htm