Instructors are frequently the targets of contentious questions related to their preferences in guns, gear, ammunition, accessories and everything else related to the concealed carry lifestyle. Sometimes this leads to a more pointed discussion as to what would be a good cartridge recommendation for a new shooter, casual shooter, experienced shooter, competitive shooter, concealed carrier and so on. But when it comes to one question, there’s only one answer: the 9mm.

It’s the oldest centerfire handgun cartridge in continuous production. The 9mm Luger, 9mm Parabellum, 9mm NATO or 9x19mm (as the cartridge is known today) is 119 years old — approaching its 120th birthday — and it has evolved and been improved on more than any other handgun cartridge in history.

When it comes to one question, there’s only one answer: the 9mm.

First adopted by the Imperial German Navy in 1904, the 9mm has since remained in continuous use by the militaries of at least 70 countries around the world. The U.S. Army finally aligned itself with the rest of its allies in 1985, transitioning from the venerable .45 ACP cartridge to the smaller — but arguably just as lethal — 9mm cartridge in the then-new Beretta M9 pistol. As the pistols evolved to the M10, M11 and, more recently, M17 and M18, the chambering has not changed. The 9mm has stood the test of time.

An Arduous Journey

Even with its obvious success and long-standing reputation for efficiency, the 9mm has had a rocky history in the U.S. It took the law enforcement community until 1968 to seriously consider the cartridge, when the Illinois State Police adopted the Model 39 Smith & Wesson pistol in that chambering. The ammunition was loaded hot and designated +P+, for which there was no pressure standard then (nor is there one now). The 115-grain hollow-point bullet of Federal’s BPLE load exceeded 1,300 feet per second, which proved to be both hard on the gun and exceptionally effective on whatever was being shot. Even so, comparatively few agencies chose to switch from .38 Special revolvers to 9mm semi-automatics.

Not until the mid-to-late 1980s did the 9mm get a boost in popular favor when some key federal agencies, including the U.S. Secret Service, the DEA and the FBI, adopted the cartridge in their new European-made pistols — principally the SIG Sauer P226, Glock 17 and Beretta 92. Smith & Wesson represented the U.S. manufacturers with its 39 and 59 series pistols. U.S. Navy SEAL teams embraced the 9mm P226 after experiencing operational concerns with the newly adopted 9mm Beretta M9 pistol. The publicity and the technology merged to boost the 9mm to the forefront of handgun cartridges once again.

But it all came crashing down in 1986 in the aftermath of the FBI’s Miami shootout. The 10mm Auto and the .40 S&W cartridges were developed to fill the power gap between the now-shunned 9mm and the .45 ACP, both of which were incorrectly thought to have been at the end of their development cycles because of their ages. It did not take long for the proponents of the 10mm Auto to realize that the cartridge loaded to full power — even in stainless steel Smith & Wesson semi-automatics — was too hot for the average agent or officer to adequately control. Even downloading the 10mm to lessen the recoil helped little to maintain the popularity of that platform.

The shift to the .40 S&W took place almost seamlessly because the cartridge was more controllable than the 10mm and was available in all the major brands of handguns suitable for law enforcement applications. In fact, the .40 S&W pistols were close, if not identical, in size to a 9mm pistol of the same brand. For the better part of 20 years, the .40 S&W remained the cartridge of choice for law enforcement and even the U.S. Coast Guard. To be fair, the .357 SIG cartridge also had a following during this time frame with the U.S. Secret Service, the Federal Air Marshals, the Federal Protective Service and numerous state and local agencies.

For the better part of 20 years, the .40 S&W remained the cartridge of choice for law enforcement and even the U.S. Coast Guard.

But the FBI once again reentered the ballistic fray to determine what round offered its agents the best advantage. Going with the premise that the objective of shooting is hitting the intended target, the FBI found that an increasing number of its agents were having a hard time qualifying and maintaining proficiency with their .40-caliber Glock 23 duty pistols. Initially, the answer to the problem was to issue those agents who were having trouble with the 23 the identical gun in 9mm, which was the Glock 19. But the FBI eventually transitioned to the 9mm Glock 19 as its duty pistol of choice.

As a result of this change and the procurement efforts of other federal agencies, the vast majority of armed federal agents today are carrying 9mm pistols. State and local agencies regularly follow the federal example, which has put the centenarian cartridge back on top of the popularity list. And it goes without saying that military and law enforcement equipment and materiel selections influence the choices of the concealed carry and personal-defense markets.

Instructors Know Best

The reasons why the 9mm cartridge is recommended as the universal cartridge for training and personal defense are many. In polling fellow firearms instructors who train a variety of students from different backgrounds and who vary in size and physical ability, we agree that the 9mm hits the sweet spot of usability for the vast majority. Usability equates to ease of handling and the ability to hit a target with single or multiple shots on demand within a reasonable amount of time. In a full- or compact-sized pistol, the low recoil of the 9mm makes the gun easier to shoot than comparable pistols in larger calibers.

Ballistically speaking, the 9mm’s trajectory is relatively flat to 50 meters, and it maintains its lethality there and beyond. Bullet weights range from 50 to 160 grains, varying from lightweight composites to conventional lead, depending on the application.

In polling fellow firearms instructors who train a variety of students from different backgrounds and who vary in size and physical ability, we agree that the 9mm hits the sweet spot of usability for the vast majority.

Logistically, the 9mm is globally more plentiful than any other handgun cartridge. Even though prices vary greatly, the 9mm is less expensive than comparable centerfire handgun loadings in the same market. This means training with your favorite personal-defense firearm is easier and universally more likely in today’s environment.

Regardless of where you are on your self-defense journey, the 9mm is the best option for self-defense. It has age, proven efficiency and a slew of other factors on its side. It has even survived a period of being ostracized in the U.S. The 9mm has secured its place in American self-defense handgunning. Don’t expect it to be phasing out anytime soon.