Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?

Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?

Of all the firearms-related quarrels, none rival the case for personal defense over which auto pistol cartridge is best. This is partly because it is very necessary for personal security, partly because people believe that there must be a single best solution, and finally because there is no definitive evidence that one works better than another. Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?

A triangle comparison with auto-pistol cartridges is ideal because you are trying to balance a three-sided equation. We have power on one side of the triangle, speed on the other and, finally, energy. This triangle exists because only so much force can be managed by a human hand, because the speed of a bullet is what makes it work, and because we would all be carrying derringers if capacity didn’t matter.Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?

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You have 3 methods to solving the problem with the 9mm Luger, .40 S&W, and .45 Auto. These cartridges each have their strengths and weaknesses. So we need to look at how each cartridge interacts with each side of the triangle in order to better understand the solution.


We have historically assessed the strength of protective handgun cartridges by kinetic energy. It is nothing more than square velocity, times the weight of the bullet. Momentum is another power factor, but a less cited one, and it is velocity in mass times. In addition different formulas exist to quantify the mythical assumption known as “stopping power.” Some of these formulas are thought to divine the capacity of a cartridge to stop bad guys by number. These numbers are merely speculation.

Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?
Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?


We discover some fascinating facts if we equate the widely considered best 9mm, .40, and .45 loads using kinetic energy and momentum. In the kinetic energy statistics, there’s very little difference, but the .45 Auto has a strong advantage from the momentum point of view. On both ends, however, strength matters (if recoil were not a concern, we would all be carrying a .44 Magnum). We see the other side of the power debate when comparing the recoil of these cartridges in fully loaded Glock 19, 22, and 21 handguns. 66% of a .45 Auto’s recoil is produced by the 9mm Luger, but it delivers 96% of its kinetic energy and 69% of its momentum.

Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?
Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?

When it comes to protective handgun ammunition, some argue that velocity does not matter. This is beyond ridiculous, of course. The .38 Special and .357 Magnum fire the same bullet, but there is no doubt it’s a better neutralizer because of the higher velocity of the .357. The sooner a bullet is moved, the more it has rotational velocity. This allows engineers to manufacture more terminally efficient projectiles that damage more tissue.

It is easy to compare capacity. This can carry more 9mm cartridges than .40 S&W, and more .40 S&W cartridges than .45 Auto, regardless of the size of the handgun. It’s hard to put an exact figure on this. However 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 by contrasting identical sized Glocks again.

Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?
Top Best Caliber for Self Defense: 9mm, .40 S&W or .45 ACP?

The 9mm has an advantage in weight, too. While 9mm handguns carry more ammunition, the lighter 9mm cartridges maintain the weight of the loaded gun below that of .40 and .45 pistols that are comparable and loaded. This means that they are easier to carry all day and they also cause lighter recoil, even though they weigh less.

The Compromise

Big bullets vs. small bullets and low velocity vs. large have always been the argument. It’s just a trade off because you’re right back to the .44 Magnum, you can’t have both high speed and a large bullet. As a compromise cartridge, the .40 S&W was designed to deliver more strength than the 9mm, with less recoil and more capacity than the .45. It has been the darling of law enforcement ever since 1990. But that’s developing.

The Veritable Gap

Measurable variations are found between these cartridges. But you can’t look at or into a cadaver, surgeons will tell you, and certainly tell which cartridge was responsible for the damage that placed it on the coroner’s slab. At the shooting end, the variations that matter most are. Does your hand suit the pistol? Can you control the rebound and quickly get precise hits? Does the gun carry enough ammo for you to solve an issue effectively? And are you able to cover it and continue to carry it all day? Given the size of the handgun they want to carry, and their ability to handle the handgun, shooters must find a handgun/cartridge combination that provides the best balance of strength, speed and energy. You’re better off spending the time trying to match the interface between the gun and the gunman than between the bad guy and the cartridge. All three cartridges are good enough, but you have to be able to fire at the end.

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Editor’s Note: This article is an excerpt from the Concealed Carry 2016 issue of Gun Digest the Magazine.

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