The Truth About Handgun Calibers and Defensive Use


Blackwater Ammunition contractor grade 9mm
Courtesy Blackwater Ammunition

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A string of recent comments on some of TTAG’s articles have made it clear there is a lot of misunderstanding out there with regard to how handgun calibers stop threats. Admittedly, it’s a subject steeped in a lot of myths and bad information that was backed by a serious lack of science for many decades. The comments include describing .380 as not much more damaging than a bee sting. Another claimed that because a typical .45 ACP round weighs 230 grains, you have to fire two 9mm rounds weighing 115 grains to stop the same threat.

With that in mind, let’s talk about how handguns actually stop threats. The first thing we have to acknowledge is that stopping power is a myth. A big one, especially in the world of handguns. It’s one of those terms that was never quantifiable and is used to often tout larger calibers as being better and smaller calibers as lacking. Yet no scientific method for measuring or evaluating ‘stopping’ power exists with regard to why a .45 ACP round is better and ending a threat than a 9mm round.

The Minimum Caliber Debate

This leads us to the argument about what the ‘minimum’ defensive caliber is or should be. That often portrays one round as being the minimally acceptable option for defensive use and anything bigger is, by definition, better.

Sometimes that minimum is 9mm. OIther times it’s .380 ACP (sometimes known as “9mm short”). In reality, I think the minimum caliber argument is silly. There are calibers I wouldn’t carry, like .25 ACP, which is admittedly small, but I wouldn’t carry .44 Magnum either. There’s a lot that goes into that other than size.

Smith & Wesson Model 69 .44 Magnum
This will stop a threat, but it’s a bit much for daily self-defense. Courtesy Austin Knudsen

The .25 ACP round is fairly anemic and doesn’t penetrate very well. The .44 Magnum packs a ton of recoil and muzzle blast, making it tough to get a good follow-up shot quickly on target. Not to mention the size of the gun and concealment concerns. That said, I would carry .22LR with the right ammo and in the right gun. I carry a .32 ACP daily and with the right ammo it can stop a threat just as quickly as a .45 ACP.

The One Thing That Matters Most With Handgun Ballistics

It’s all about penetration. Handguns only have one wounding mechanism, and it’s the wounds caused by what the bullet impacts. There are no secondary wounding effects from standard handguns. Handguns can’t generate a shock that causes other wounds. There is no significant energy dump either. (Yes, ‘handgun’ is a big category, but we are talking typical handguns here, not AR pistols.)

A pistol projectile should be able to penetrate at least 12 inches of 10% ballistic gel that’s properly calibrated. Humans aren’t jelly, but the FBI, who established that standard, found that if a round can penetrate that deep in proper ballistic gel, it can reach the vital organs that, when struck, can stop a threat. Calibers like .380 ACP, .32 ACP, and .22LR can all do that with proper projectile selection.

Stopping a Threat

In self-defense, there are only three ways to stop a threat.

Psychological Stop – The bad guy decides the fight is over. The round doesn’t have to strike something to kill the attacker, but simply being hit changes its mind. You may not even have to pull the trigger. A psych stop can happen as soon as you pull the gun.

Blood Loss – The slow way to stop a threat is to hit something that causes lots of bleeding in your attacker. The body works best when it has all of its blood, and the more of that someone loses, the more likely they are to lose consciousness and eventually assume ambient temperature.

Vital Strike – This is when you hit something vital like the brain, the heart, or maybe the lungs a few times. That is the quickest way to stop a threat.

Training: 5 Ways to Find the Right Firearms Instructor
Courtesy NSSF

A .45 to the brain is no different than a .22LR to the brain. (Also, contrary to lots of online lore, a .22LR round doesn’t “bounce around” causing additional wounding effects any more than any other round does.) The same goes for heart, lungs, etc. The size of the projectile doesn’t matter as much as the projectile’s ability to get there. If the projectile can get there, it doesn’t matter much how big it is. What matters more is the shooter’s ability to place rounds where they will be most effective.

Why Don’t We All Just Carry .32 ACP Then?

Because it’s expensive. It can have rim lock issues, too. The real question is, why is 9mm the round gun owners and the industry have seemed to settle on? Obviously, it works well as a cartridge. It’s also incredibly common and is also the NATO standard. The 9mm round has always been affordable, easy to find, and allows for relatively high capacities in handguns. In hollow point options, it’s quite impressive and very capable.

For the duty world, 9mm does pretty well getting through soft cover and thin barriers. Glass, car doors, light wood, heavy clothing, etc., aren’t typically worries for the average concealed carrier, but for cops and soldiers, it matters. The main reason why we use 9mm over other rounds is because it’s a great jack-of-all-trades.

9mm ammunition ammo
9mm ammunition (Dan Z. for TTAG)

What advantage do rounds like the .40 S&W, .357 SIG, and 10mm offer over 9mm or other calibers like the .380 ACP? They definitely handle barriers better. They tend to penetrate deeper, but when does that extra penetration matter? If 9mm can reach vitals, why would a round need to go deeper?

In the 1986 Miami Shootout, which was the catalyst for the FBI’s adoption of 10mm, a 9mm round stopped an inch from the heart of one of the criminals. Defensive 9mm ammunition in the mid-80s wasn’t nearly as capable as it is now, and the round initially went through the bad guy’s arm, which gave it more meat to contend with. The .40 S&W, .357 SIG, and 10mm’s deeper penetration can be beneficial in those odd-angled shooting scenarios.

The key word is ‘can’ and not ‘will.’ It’s never guaranteed and too many variables exist to say it will always work.

What About Expansion?

If you have a round that can penetrate deeply enough into an attacker, then the next step is to choose the right defensive projectile. For the vast majority of rounds, a jacketed hollow point bullet is the way to go. A JHP gives us expansion and expansion is nice.

A bigger hole is a bigger hole. If all handguns can do is damage tissue as they travel through it, then the larger expanded projectile is better than one that expands less or not at all.

Does expansion make enough of a difference to stop a threat if the shot isn’t placed in an area that matters? No, not really but it might make a threat bleed out faster.

Ammunition spread expansion copper
Dan Z. for TTAG

Another real benefit of JHP ammunition is the fact it doesn’t tend to over-penetrate and zip through a target. Bullets that go through an attacker and out the other side can easily harm another person who isn’t an attacker. With that said, there are certain hollow point projectiles that are gimmicks. With all of that in mind, yourn job is to choose the right hollow point.

Hollow point ammunition can be detrimental in some calibers and cartridges in specific guns. My beloved .32 ACP sucks with JHPs. JHPs in .32 ACP expand too early, and that causes the round to slow down too fast, preventing adequate penetration. It might work better from a longer barrel, but longer-barreled .32 ACPs aren’t very common. The same goes for .22LR in pocket pistols. You want an FMJ to reach adequate penetration.

Bigger Bullets and Bigger Threats

Keep in mind we’re talking entirely about human-based threats here. If you have to fend off bears, well, I’d then carry a .44 Magnum or a 10mm with some hard cast lead rounds.

Montana black bear
(Seeley Oblander via AP)

Bears tend to be bigger, thicker, and more difficult to penetrate than anything the FBI contemplated when it created that gel block testing standard.

To recap, for defensive use, size doesn’t matter as much as penetration and shot placement. There is no (or not much) such thing as stopping power, hydrostatic shock, or energy dumps with handgun rounds.

No, you don’t have to shoot someone twice with a 9mm because the bullet weighs half as much as one in .45 ACP. A .380 ACP to a vital organ can stop a threat just as successfully as a 9mm, .40 S&W, or .45 ACP, etc. Expansion is nice, but size never tops shot placement or penetration.

If it can penetrate adequately and you can shoot it straight, then carry it with confidence.

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