10mm vs 9mm: Does 1mm Make a Difference For Your Self-Defense Handgun?

When it comes to self-defense, many shooters hold to the belief that you should shoot the caliber that has the best ballistics and the most stopping power that you can handle. These shooters like to favor a larger caliber bullet, such as the 10mm Auto.

Other shooters believe that the ideal defense round should be lightweight and low recoil, allowing for accurate and quick follow-up shots as modern jacketed hollow points (JHP) have made the caliber debate moot. These are typically your 9mm Luger concealed carry permit holders.

The 9mm vs 10mm caliber debate is an interesting one as these two handgun rounds are extremely different from each other, despite their bullet diameter only being separated by 1mm. And it begs the question, is bigger actually better when it comes to self-defense?

In this article, we will compare the 9mm Luger and the 10mm Auto under the auspices of determining which round will be the better choice for personal defense.

What’s the Difference Between 9mm and 10mm?

When new shooters first hear about the 9mm Luger and the 10mm Auto, they often think that they are very similar cartridges. I mean how much difference can 1mm make?

Well, the answer is: Quite A Bit!

Sure, the bullet diameter is only 1mm different, but the bullet weight, muzzle velocity, and ft-lbs of energy are considerably different when comparing 10mm vs 9mm.

So, when you’re loading up your favorite semi-auto, which one do you go for? Do you go for your trusty Glock 19 or is a Glock 20 your go-to personal defense handgun?

In the next few sections, we will break down the differences between the 10mm Auto and the 9mm Luger to give you a better idea of which handgun caliber will be best for your needs.

Case Specs

Looking at the case spec chart, we see that the 9mm Luger and the 10mm Auto are extremely different.

The first thing to note is that the 10mm fires a 40-caliber bullet (0.401” bullet diameter) while the 9mm Luger fires a smaller, 9mm bullet (0.355” bullet diameter). Furthermore, the case capacity of the 10mm round is just short of double that of the 9mm, meaning that more gunpowder can fit into the 10mm allowing it to fire heavier bullets at a higher muzzle velocity.

Simply put, the 10mm round is bigger in every category compared to the 9mm Luger. With the large case comes higher pressure, velocity, ft-lbs of energy, and recoil.

All those specs lead to the biggest argument for the need for 10mm ammo, Stopping Power which we will cover in the next section.

Stopping Power

Stopping Power is one of those ubiquitous terms that gets thrown around gun store cases and internet gun forums all the time. It cannot be quantified as it is the concept of how effective a bullet is at stopping a threat.

Proponents of the 10mm round will point to the fact that it is a larger caliber, shoots heavier bullets at higher speeds and with increased muzzle energy. In theory, the bullets should leave a wider permanent wound channel and therefore cause increased blood loss if a critical organ is not damaged.

However, with modern hollow points, the gap between handgun calibers has been closed significantly when it comes to permanent wound channels.

On average, a 10mm JHP round will expand between 50-100% of its starting diameter. However, the same can be said for the 9mm Luger as well. So, if we assume maximum expansion between the 10mm vs 9mm, we are talking about 0.8” vs 0.7”. That’s not exactly a huge difference.

All modern personal defense ammo should expand with good reliability and repeatability through heavy clothing. These hollow points include the Hornady XTP, Remington Golden Saber, Speer Gold Dot, Winchester Ranger-T, and Underwood Jacketed Hollow point ammo.

FBI ballistic gel data suggests that penetration for jacketed hollow point ammo is almost identical for 10mm and 9mm ammo.

If the permanent wound cavity is similar between 9mm vs 10mm, then what is the difference?

There is some suggestion that the kinetic energy transfer that the target receives can somehow incapacitate the target or remove their will to fight. This is one of the primary arguments that proponents of the 357 SIG use for justifying their choice over 9mm.

There is a significant difference in terms of kinetic energy between the 10mm Auto and 9mm Luger, with the 10mm delivering almost double the ft-lbs of energy at the muzzle.

However, the kinetic energy transfer argument cannot be quantified, since the “will to fight” will be different between bad guys depending on multiple factors, including any illicit substances they have in their system (I’m looking at your Mr. PCP user).

There’s no doubt that the 10mm round will “hit harder” but does this really stop an attacker? Supporters of the 10mm will say yes, 9mm fanboys (and girls) will say that shot placement is more important.

The final potential difference is the size of the temporary wound cavity which occurs when a bullet impacts soft tissue. Sometimes referred to as a stretch cavity, the temporary wound cavity is caused by the rapid transfer of energy to the target from the bullet impact.

Highspeed camera footage clearly shows the 10mm Auto producing a larger temporary wound cavity than the 9mm. There are some theories that this temporary wound cavity can cause additional tearing/shredding of soft tissue in the target and therefore increase blood loss.

This is referred to as hydrostatic shock and is one of the primary reasons for the effectiveness of the 5.56 NATO (a lighter bullet going at ridiculously high velocity).

However, many ballisticians point to the fact that handgun bullets simply do not travel fast enough to cause sufficient hydrostatic shock to cause any permanent damage. So, we are still left with the question of does any of this matter? Does the kinetic energy dump aid in stopping a bad guy or is shot placement all that matters?

There may be other forces involved here that cannot be calculated or quantified by ballistic gel, and as I’m not willing to sign up to get tagged by a 10mm nor a 9mm and share my feelings on the matter, I think the topic of Stopping Power will remain unknown with current data.

However, as the 10mm has about double the kinetic energy of the 9mm Luger, we will give the edge in Stopping Power to the 10mm with a bit of an asterisk.

Recoil

If there was controversy in terms of Stopping Power in the section above, Recoil is going to be considerably more cut-and-dry.

As we mentioned earlier, the FBI moved away from the 10mm round as the heavy recoil was simply too much for agents to handle and maintain quick follow-up shots.

For your standard 10mm self-defense loads, shooters will have to endure recoil in the range of 10-12 ft-lbs of punishment to their wrists. In contrast, 9mm shooters will only have to fight off 4 to 8 ft-lbs of recoil.

Essentially, the 9mm will recoil on average 50% less making it easier for shooters to get their sights back on target for follow-up shots.

The punishing recoil of 10mm loads also causes more wear and tear on the handgun itself, requiring parts to be replaced more frequently than with a 9mm handgun.

Recoil can be mitigated somewhat by using a heavier gun, there’s no denying that an all-steel Colt Delta Elite in 10mm will have less felt recoil than a polymer-framed Glock 20.

Furthermore, bullet selection plays a role as a lighter bullet will have less recoil than a heavier bullet.

However, there is no denying that the 9mm Luger has significantly less recoil than the 10mm, making the 9mm easier to shoot and shooters can become proficient with it quicker.

The 9mm wins this one by a country mile.

Magazine Capacity

Magazine Capacity is another win for 9mm Luger as it is an overall smaller round as we saw in the Cartridge Specs section.

Your standard Glock 17 magazine can carry 17+1 rounds of 9mm Luger into battle. The Glock 20 magazine can carry 15+1 rounds of 10mm Auto, which is not insignificant by any stretch of the imagination.

However, the 9mm Luger clearly is the winner in terms of magazine capacity.

Hunting

Hunting is one category where the 10mm really shines as recoil is less important during hunting as follow-up shots are rarely used.

The 9mm and 10mm can both be used for smaller varmints with great success. However, when we start moving into feral hogs, deer, and even black bears, the 10mm is clearly the superior choice.

Its heavier bullets will be more effective at punching through thick hide and bone, making for a more humane kill. Furthermore, the flatter trajectory of the 10mm will make it the better choice for longer hunting shots.

If you’re going out into the field hunting for 4-legged critters, then the 10mm is the better choice.

Self-Defense and Concealed Carry

This one is going to be somewhat controversial, but I’m going to go out on a limb and say that the 9mm Luger is the better choice for self-defense and concealed carry. Before you start writing your email to tell me how I’m wrong, let me explain why.

For concealed carry, there’s no denying that 9mm handguns are going to be lighter than the 10mm variety. Furthermore, many shooters will opt for compact or subcompact handguns as they are easier to conceal and carry.

Now, if we are shooting smaller guns, the amount of recoil you will feel is going to be increased as there is less firearm mass to soak up that recoil impulse.

The Glock 26 subcompact 9mm is extremely popular for CCW permit holders as it has reasonable magazine capacity, is lightweight, and the recoil is manageable.

For concealed carry, a 9mm allows you to carry more ammo with a lighter handgun which means you’ll be more likely to carry it consistently.

However, one of the biggest considerations that need to be at the forefront of your mind when selecting a caliber for concealed carry is overpenetration.

Anyone who owns a firearm for personal defense needs to remember that every bullet you fire has a lawyer attached to it. This saying means that you are legally liable for every bullet you fire.

The simple fact is that accuracy will suffer during a firefight, mostly due to panic and the resulting adrenaline dump all shooters will experience. In this case, the Fight or Flight Response takes over and, as an instructor once told me, we revert to our lowest level of training and muscle memory.

Every shooter believes that they will be able to stack rounds in a tight concentric circle on the center mass of the bad guy with John Wick style precision. However, police shooting reports do not support this concept and suggest that combat accuracy is around 20-30%.

Therefore, we need to consider overpenetration as a hit to the thigh or arm is very likely to pass through the bad guy and could potentially hit an innocent bystander.

In this case, the added power of the 10mm Auto actually works against itself making it more prone to overpenetration. This is also true indoors as a 10mm can easily pass through sheetrock and external walls into your neighbor’s apartment or home, potentially causing bodily harm to them (which you are liable for).

Of course, the 9mm has the potential for overpenetration as well, but overall it will be less than the 10mm.

The final point for self-defense is follow-up shots. The age-old WWII concept of one shot, one kill has long since been proven folly when it comes to handgun cartridges.

Unless your shot placement is perfect (hits in the Fatal T), it is unlikely a handgun engagement will be resolved with a single shot. Therefore, the shooter who can put more rounds on target faster will typically win the fight.

With its lower recoil and lower potential for overpenetration, the 9mm is the better option when it comes to self-defense against 2-legged bad guys.

Bear Defense

If you note the last sentence of the previous section, I referenced 2-legged bad guys. The game changes when we get into bear country.

Overpenetration is a huge concern in urban or suburban environments, but in the woods, I want as much penetration as I can get. And if I’ve got an angry Grizzly or Boar bearing down on me, I’ll be glad to have a fully loaded Glock 20 and 15 rounds of 10mm FMJ ammo ready to go.

Predators such as bears and feral hogs are incredibly tough, they have thick hides, bones and sinew that support their large frames. This means that you need a bullet with a lot of power to punch through the skull to hit the central nervous system or crack the ribs to get to the vitals such as the heart and lungs.

A 10mm Auto is perfectly suited for this and there is a reason that the top-selling semi-auto handgun in Alaska is the Glock 20.

Can you defend yourself against a bear with 9mm? Yes, and some have.

But just because you “can” do it does not mean that it is the ideal choice. A 9mm simply does not have the energy to penetrate through thick bear skulls and bones consistently and you will need ideal shot placement to survive a bear attack with a 9mm.

The 10mm round is the clear bear cartridge of choice if you are going to use a semi-auto handgun. However, a 41 Remington Magnum or 44 Magnum revolver is often the de facto choice in bear country.

Continue reading about the differences between 10mm and 9mm ammo here.