With auto-pistol cartridges a triangle analogy is appropriate because you’re trying to balance a three-sided equation. On one side of the triangle we have power, on another speed, and finally, capacity. This triangle exists because a human hand can only control so much force, because a bullet’s speed is what makes it work, and because if capacity didn’t matter we’d all be carrying derringers.
With the 9mm Luger, .40 S&W, and .45 Auto, you have three approaches to solving the problem. Each of these cartridges has its strengths and weaknesses. So, to better understand the solution, we need to look at how each cartridge interfaces with each side of the triangle.
Historically we’ve measured defensive handgun cartridge power by kinetic energy. It is nothing more than velocity squared, times bullet weight. Momentum is another, though a less referenced, measure of power and it is mass times velocity. Additionally, there exist various formulas for calculating the mythical assumption known as “stopping power.” Some of these formulas are thought to divine, by number, a cartridge’s ability to stop bad guys. Those numbers are simply conjecture.
Some argue velocity doesn’t matter when it comes to defensive handgun cartridges. This of course is beyond absurd. The .38 Special and .357 Magnum shoot the same bullet, but due to the higher velocity of the .357, there’s no question it’s a better neutralizer. The faster a bullet is pushed, the more rotational velocity it has. This helps engineers develop more terminally effective projectiles that damage more tissue.
Capacity comparison is simple. Regardless of the size of the handgun, it will hold more 9mm cartridges than .40 S&W, and more .40 S&W cartridges than .45 Auto. Putting an exact number on this is impossible. However, by again comparing similar sized Glocks, we see the 9mm (Glock 17) holds 17 rounds, the .40 S&W (Glock 22) holds 15 rounds, and the .45 Auto (Glock 21) holds 13 rounds.
The argument has always been big bullets versus small bullets and low velocity versus high. It's all a trade off—you cannot have both high velocity and a big bullet because you’re right back to the .44 Magnum. The .40 S&W was built as a compromise cartridge to offer more power than the 9mm, with less recoil and more capacity than the .45. Since 1990 it has been the darling of law enforcement. But that’s changing.
It appears the FBI, the organization responsible for the .40 S&W due to its dissatisfaction with the 9mm, has now concluded that the 9mm solves the triangle better. This is largely because it’s easier to shoot faster and more accurately, by more agents. Since agents are people, too, the conclusion applies to regular folk just the same. The FBI also acknowledges modern bullet technology has all but eliminated the terminal performance differences between these cartridges. In short, smart guys who make bullets figured out how to utilize the ballistic differences of each cartridge to practically equalize their terminal effectiveness.
The FBI has realized the shooting part is more important the anything else. Misses or bad hits don’t stop fights. The focus has wisely shifted from ballistics to marksmanship! What a novel concept.
The Real Difference
There are measureable differences between these cartridges. But surgeons will tell you, you cannot look at or into a cadaver and definitively tell which cartridge was responsible for the damage that put it on the coroner’s slab. The differences that matter most are on the shooting end. Does the pistol fit your hand? Can you control the recoil and get accurate hits, fast? Does the gun hold enough ammunition for you to effectively solve a problem? And, can you conceal it and manage to carry it all day? Shooters must find a handgun/cartridge combination delivering the best balance of power, speed and capacity, given the size of the handgun they want to carry, and their ability to manage that handgun. You’re better off spending your time trying to balance the interface between the shooter and the pistol than between the cartridge and the bad guy. All three cartridges are plenty good, but in the end, you gotta be able to shoot.
Editor's Note: This article is an excerpt from the Concealed Carry 2016 issue of Gun Digest the Magazine.