The 9 millimeter and 45 ACP debate is one of the most common, and heated debates in the firearms community. Both sides have some solid arguments, and it can be tough to figure out which is best. Of course, some guys will never change their opinion on which is better, but if you are looking for genuine content to figure out which one you should go with, you will love this article.

Estimated reading time: 23 minutes

9mm vs 45 ACP: The Greatest Pistol Caliber Debate

So which one is better? If you go back 40 + years, you will find that just about every American soldier had a 45 caliber 1911. Nowadays, law enforcement officers and soldiers alike are using the 9mm in Glocks, Berettas, and Sigs. Of course, they do not all use 9mm, but it is very common. 

For starters, the 9mm and 45 ACP are both great calibers. Each of them are battle proven and have been used for many decades. However, each of them have an advantage over the other in multiple areas. After a lot of research, my conclusion is that there is not one caliber that is better than the other in every situation. Sometimes a 9mm is better, other times the 45 ACP reigns king. It all depends on your application.

To prove that to you, I am going to go over every single aspect of these rounds and show just how much better one is than the other if they are better at all. Let’s start with a little background on each of these calibers.

What is 45 ACP? America’s Two-Time World War Winning Handgun Cartridge

During the Moro Rebellion, part of the Philippine–American War(1899-1913), soldiers using the .38 Long Colt reported that the round had a lack of stopping power and they needed something that was better and stronger for their sidearms.

So John Moses Browning created the rimless, straight walled .45 Automatic Colt Pistol(ACP) in 1904. This was a cartridge that was designed to be fired out of his new semi-automatic pistol that would eventually become the government issued M1911A1. This cartridge was originally 230 grains and traveled at a speed of 830 feet per second.

The M1911A1 was a huge success and did a much better job than the Colt double action revolvers chambered in 38 Long Colt that soldiers were using. Along with the new semi-automatic 1911, the 45 ACP skyrocketed in popularity. The 45 ACP would also start being used in the Thompson submachine gun in the military between 1938 and 1971.

The M1911A1 and the 45 ACP were issued in 1911, and had continued use through the century, but were eventually replaced by the 9mm Beretta M9 in 1985. Even still, the 1911 was used in 25 wars/conflicts around the world and was used extensively by the United States and NATO in both World Wars. While it is rare, the 45 ACP can still be found in use in a few specialized units throughout the American military. 

Nowadays the 45 ACP comes in all sorts of load variations and is used extensively for self defense and sport shooting. Its hollow point loads are very popular for self defense, and its full metal jacket rounds are often used in competitive shooting.

What is 9mm? The German Military Powerhouse

The 9mm goes by many names. A few of them are 9mm, 9x19mm parabellum, 9mm luger, or 9mm parabellum. All of these refer to the same cartridge. Anyways, in 1901 an Austrian firearms maker named Georg Johann Luger created the 9mm cartridge.

He originally made this cartridge to work with his Luger pistol which was very popular. The 9×19 parabellum was also not the first design he came up with to work with his pistol. The 9×19 parabellum is actually a derivative of Luger’s 7.65x21mm parabellum which itself was a derivative of the 7.65×25mm Borchardt.

After he was happy with the cartridge, Luger presented the new round to the British Small Arms Committee, as well as three prototype versions to the U.S. Army for testing at Springfield Arsenal in mid-1903. The Imperial German Navy adopted the cartridge in 1904, and in 1908, the German Army adopted it as well.

Germany especially liked the cartridge and used it extensively during World War II. They used it because it had excellent penetration and power, but was considerably smaller than other cartridges, which means they were able to save resources while producing it. 

At one point Germany even replaced the lead core of the 9mm with iron to save money. Instead, they had an iron core with a lead cover and a black jacket. They eventually went back to lead cores and copper jackets in 1944.

After World War I, the 9x19mm parabellum started to spread in popularity. It was reliable and effective, so it found its way into thousands of pistols and automatic submachine guns. Now it is the standard issue caliber of the US military and NATO in the Beretta M9 and SIG Sauer M17.

9mm vs 45 ACP: Differences Between 9mm and 45 ACP

Although the 9mm and 45 ACP are two opposite ends of a spectrum, they are actually fairly comparable in terms of energy. There are many different factors to look at and compare, and we will talk about all of them, but here are a few tables we will reference first that also summarize our findings. 

Energy Comparison – Velocity(ft/sec) / Energy(ft-lbs)

Caliber & TypeGrainMuzzle25 Yards50 Yards75 Yards100 Yards
9mm FMJ1001240/3411147/2921075/2571019/230973/210
9mm JHP1001125/2811057/2481003/224960/205922/189
9mm FMJ1151158/3431098/3081050/2811010/260975/243
9mm JHP1151158/3431091/3041038/275994/252956/234
9mm SCHP +P1151125/3231078/2971039/2761005/258975/243
9mm TMJ1151200/3681145/3351098/3081059/2861024/268
9mm FMJ1241131/3531081/3221039/2981003/277972/260
9mm JHP1241126/3491075/3171031/292995/272963/255
9mm JHP +P1241220/4101146/3621085/3241036/296996/273
9mm FMJ1471000/326976/311953/297933/284914/273
9mm JHP147990/320964/303940/288917/274897/263
9mm TMJ147985/317957/299932/284909/270888/257
45 ACP FMJ185910/340885/322863/306842/291822/277
45 ACP SWC185770/244735/222703/203672/185642/170
45 ACP JHP185980/395945/367914/344886/323860/304
45 ACP FMJ230852/371834/356817/341801/328785/315
45 ACP JHP230898/413878/394860/378841/362825/384
45 ACP JHP +P230963/475940/451919/431900/413880/396
Data from https://www.ammunitiontogo.com/lodge/

9mm vs 45 ACP Summary Table

Caliber9mm45 ACP
Size & ShapeSmaller, better penetratingBigger, more blunt shape
Velocity & EnergyFaster, less energySlower, more energy
Stopping PowerLess stopping powerMore stopping power
PenetrationVery good at penetratingModerately good at penetrating
RecoilLighter recoilMuch more recoil
Magazine CapacityHigher capacity, 30% moreLess capacity due to size
Suppressed Performance Similar Performance Similar Performance

45 ACP Vs. 9mm Ballistics

One of the most important aspects of any cartridge is its ballistics. For starters, ballistics is the science of projectiles and firearms. We use this term to define how the bullet flies, and also how it impacts its target. Technically velocity, kinetic energy, bullet drop, bullet design/aerodynamics, and wounding channels all fall under the ballistics umbrella, so we will talk about them all here.

If you look at the “Energy Comparison” table above, you will see many different kinds of 9mm and 45 ACP rounds and their velocity and energy over a distance. For most situations, it is safe to look at the 25 yard stats. Most self defense situations occur at less than 15 yards, and SBR’s or rifles that are chambered in 9mm or 45 ACP that you would use to shoot farther distances will have different ballistics due to their increased barrel length.

This is the biggest talking point in the 9mm vs 45 ACP debate. Would you rather have small and fast, or big and slow? Which one is better? Well, they are both good in different situations. As you can see, every grain and bullet design has different stats.

45 ACP Vs. 9mm Size & Shape

One of the most important factors in ballistics is just how big the projectile is. There are two things that we look at when considering the size of a bullet, the weight(in grains), and the caliber/diameter. 

45 ACP is a 45 caliber bullet, which means it is 0.45 inches in diameter. This cartridge was made in the United States, which is why it uses inches. On the other hand, the 9mm was made overseas, so it uses the metric system. The 9mm measures 9 millimeters around, which is about 0.3543 inches. From these numbers, you can see that the 45 ACP is about 27% bigger around than the 9mm.

Other than ballistics, the size of a cartridge is going to influence how big your pistol needs to be. That is why you can buy super small pocket pistols in 380 ACP, or very tiny derringer in 22 mag. The smaller the round, the smaller the gun can be. 

That also means the bigger the round, the bigger the gun needs to be. So to have a pistol in 45 ACP, you are going to need a larger gun which can be a disadvantage for people with smaller hands. Plus it will also be harder to conceal. Lastly, a bigger bullet means you can have less of them in the same space, limiting capacity.

The shape of a bullet also has a lot of effect on its ballistics. If we are talking about full metal jackets, 9mm’s are generally more pointy and longer than the 45 ACP. Longer, pointier bullets are a lot more aerodynamic, which means they experience less drag while in flight and can fly farther. 

Hollow points hinder the flight of these bullets because they cause a lot more drag. That is why you can see that they have a lot less energy over a distance when compared to an FMJ of the same size in our energy table above. One thing manufacturers have done to combat this is add a plastic insert to their hollow points, which makes it fly more like an FMJ, but still impact like a hollow point.

The design of bullet shapes is a whole science in and of itself, and we could talk for a really long time about it. The skinny of it is that pointer bullets usually go farther and penetrate better, all other variables held constant. 

9mm Vs. 45 ACP Velocity & Energy

For starters, the 9mm is going to go faster than the 45 ACP. However, the 45 ACP will always be bigger than the 9mm. When we calculate energy, we are actually calculating something called kinetic energy. This is the energy an object has while it is in motion. We calculate it with the formula energy = 0.5 * mass * velocity * velocity. Velocity is squared here and is the overriding factor for the energy. 

If we generalize the data a little, we can estimate the average 9mm flies at around 1100 feet per second and has around 330 foot pounds of energy. While the 45 ACP flies at around 900 feet per second and has around 370 foot pounds of energy. Cool, but what does any of that mean?

Well, the data reinforces the idea that 9mm is fast and small, and 45 ACP is slower and bigger. This energy number we came up with is what will estimate your knock down power. Knock down power is more or less a made up word, and there is not a calculation for it. The idea we have of knock down power also does not align perfectly with our energy calculation. We can have two projectiles, one small and fast, and the other much bigger but slower, and they could possibly have the same amount of kinetic energy.

45 ACP vs 9mm: Stopping Power

Threats that are shot with small and fast bullets, oftentimes do not even know they are hit. Of course, this also has a lot to do with adrenaline, but small and fast bullets often go through a target without being noticed for a few moments. On the other hand, if you were to hit a threat with a big and slow crowbar, they would definitely feel that immediately. 

Obviously, I am not trading my concealed carry gun for a crowbar, but my point is, small and fast can take a moment to be noticed, while slow and big does a much better job at stopping a target immediately.

45 ACP has an awesome reputation for putting out a whole lot of stopping power. They were so powerful in fact, that as punishment, US soldiers used to make Vietnam prisoners stand with their arms held out to the side,  then the soldiers would shoot the prisoners in the hand with their 1911’s. This would make the prisoner turn a complete flip, just by getting hit in the hand. 

It is a gruesome story, but it is true. It also shows just how powerful these slow rounds can be. A 9mm would likely go through the hand and knock the prisoner over, but would likely not do much else.

If you want to have something with the most “knock down power” then the 45 ACP is the way to go. 9mm is an effective cartridge but is much better at penetrating than knocking down. However, penetration also has its own advantages.

9mm Vs. 45 ACp Penetration

So 45 ACP won when it comes to stopping power, but what about penetration? Well, it turns out they are just about opposites of one another. You can not have a ton of stopping power and penetration. We already talked about how 9mm was much faster than the 45 ACP, well to penetrate things better, you need speed. 

But why would penetration be better than stopping power, or vice versa? Well, if you are concealed carrying and want to be able to effectively shoot through concealment, a 9mm would be more effective on the other side of that concealment than a 45 ACP.

This is very useful if you have to shoot through things like cars, walls, or even metal. This means if you encounter a threat, you can easily shoot through any cover they take and be able to take them out. Granted, you can still do this with a 45 ACP, but it will be less successful on average.

However, you may not want your bullet to penetrate as much if you are in your home, or apartment complex. In that situation, the bullet could pass through the threat, wall, and into another person’s dwelling. Which is obviously bad. In this situation, hollow point 45 ACP cartridges would be better.

There have also been a ton of videos made on youtube that show just how much better than 9mm is at penetrating than the 45, and to be honest they are better at showing it than the written word. Here is a quality video that I liked on Youtube:

45 ACP Vs. 9mm Recoil

It is no secret that the 45 ACP has much more recoil than the 9mm. I really wanted to make a big table out of it, but recoil is actually quite difficult to calculate. Not only does it depend on the energy of the cartridge, but also the weight of your firearm. So if I wanted to make a table like the energy table, it would have hundreds of entries for all of the different grains, bullet types, and then pistol sizes. Plus I know you would scroll past it anyway… Instead, I am just going to look at a couple of the most popular rounds from 9mm and 45 ACP at some standard pistol weights for that cartridge.

9mm vs 45 ACP Recoil Comparison


Caliber

Grain

Velocity(ft/sec)
Pistol Weight(lbs)Recoil Energy(ft-lbs)Recoil Velocity(ft/sec)Normalized Recoil Score
9mm115115523.811.11.556
9mm124115724.411.91.868
9mm11511551.55.2152.573
45 ACP18510402.56.813.22.848
9mm12411251.56162.980
45 ACP2309162.57.513.93.179
45 ACP18510002.257.714.83.373
45 ACP2308502.257.9153.467
Data from https://www.chuckhawks.com/handgun_recoil_table.htm

The most important column here is the “Normalized Recoil Score”. This is a formula / idea that I got from sportsmans.com and their rifle recoil table. 

My normalization is based on a 0-10 range. I used the rest of the data from the Chuck Hawks table, so zero represents the cartridge with the least recoil (.32 S&W Long) and 10 represents the cartridge with the most recoil (45 Colt +P). I stopped my data at 45 Colt +P. This is because large cartridges like the 475 Linebaugh or 500 Linebaugh were outliers for the most part and made the 9mm and 45 ACP normalized scores very small.

I started this calculation by making a recoil score with the recoil energy and recoil velocity. I used them to make a weighted average at a ratio of 7:3 respectfully. This average will be referred to as X. 

Then I used a normalization formula based on a range. a represents the bottom of the range, 0 and b represents the top of the range, 10. The Xmin and Xmax are the recoil scores for the previously mentioned 32 S&W Long and 45 Colt +P.

What this data can tell you is how one cartridge out of a particular weight of a gun, grain, and speed compares to another. Looking at plain recoil energy stats does not really tell the average person much. So on our select number of cartridges we chose to look at, the one with the least amount of recoil is the 115 grain 9mm out of a 2 pound pistol.

If you pay attention to the 9mm entries alone, you will notice that the rounds fired from the heavier gun had less recoil. This is something that we generally accept, so it is good our data supports that assumption and real world experience. You can also see that the heavier grain bullet had more recoil as well. These patterns are repeated in the 45 ACP entries.

Nonetheless, you can see that the 45 ACP generally has more recoil than the 9mm. Although in the middle of the table, you can see the heaviest grain 9mm out of the lightest gun has more recoil than the lightest grain 45 ACP out of the heaviest gun. These are two extremes for both calibers.

Why Recoil Matters

I was more or less just having fun with the tables and science because you really do not need all of that proof to know that a 45 has more recoil than a 9. Nonetheless, recoil is important for a variety of reasons.

The most important of those is accuracy. More recoil leads to less accuracy in general. Sure you can train to counteract the recoil and be more accurate, but it is much easier to be accurate with a gun that has less recoil. 

According to the FBI, law enforcement officers are 20 to 30% accurate. Generally, their first shot is the most accurate, and the kick from the pistol normally makes their second shot go a little high. So with less recoil, they can ideally keep their groups closer together while in the moment.

Another important thing about recoil is its ability to cause a jam. We all do our best to practice using a proper grip, but in the moment you may not pull your pistol out perfectly, or may even have to use a single hand to shoot. This poor grip can cause something called limp wristing. 

Limp wristing means the user did not have a tough enough grip to allow the slide to transfer most of its energy horizontally. Instead, the user allows the barrel to kick up, and the slide is pushing back in a nearly vertical fashion. This makes the slide fail to cycle and will cause a malfunction, effectively putting the firearm out of the fight until the malfunction is cleared.

Since a 9mm has less recoil, this is less likely to happen in the heat of the moment. It is not the only reason, but it does play a part as to why the US military and law enforcement departments have chosen to go with the 9mm. This cartridge has been observed to have this malfunction less often than the 45 ACP.

Lastly, a pistol with less recoil is easier to master for a beginner. I own and often shoot both 9mm and 45 ACP, but my first pistol was a 9mm and was very easy to shoot. This allowed me to learn the basics of using a pistol easier and let me create better habits while shooting, instead of flinching at the recoil of a 45 ACP. 

9mm Vs. 45 ACP: Magazine capacity

When you look into this 45 ACP and 9mm debate, a major point from the 9mm side is that you can have many more rounds in your magazine when you are using the smaller 9mm. That is true and can be a major advantage sometimes.

 If you look at the 45 ACP Glock 21, it is just slightly larger than the 9mm Glock 17. They are both standard size Glocks, but the G21 holds 13 rounds in its magazine and the G17 holds 17. That’s an extra 4 rounds, or 30% more rounds,  that you can use to shoot whatever you are shooting. 

Of course, this is highly dependent on the pistol you are using, but these two Glocks are about as close as you can get to being the same pistol in both calibers. This sort of changes the argument from small and fast or big and slow to more of small and fast or less of big and slow. 

I have mostly ignored this part of the argument until now, because I think looking at the actual performance of the round is more important. However, a lot of the aspects we have discussed are stacking up in favor of the 9mm if you want to be able to penetrate and use it in many situations. More rounds in your mag is just a cherry on top, however, that may not matter in a few states. 

Nine states and the District of Columbia have enacted laws banning large capacity ammunition magazines: California, Colorado, Connecticut, Hawaii, Maryland, Massachusetts, New Jersey, New York, and Vermont. Most of these states limit magazines for any type of firearm to 10 rounds. You can easily get a 45 with 10 rounds, and the same goes for 9mm so this portion of the argument does not apply as much to people who live in these states.

Even still, if your 45 ACP and 9mm both hold 10 rounds, you can bet that the 9mm is going to be smaller. You can get some fairly small pistols like the Glock 43X that are slim, very easy to conceal, and hold 10 rounds. So even though you will have the same amount of rounds, the 9mm can be much smaller and easier to conceal if you want it to be, whereas the 45 ACP will be closer to a standard size pistol. 

45 ACP Vs. 9mm Suppressed

The speed of sound is 1125 feet per second. If you go back up to our Energy Comparison table, you will see a bunch of velocities for our selected 9mm and 45 ACP cartridges. If you pay attention, you will see all of the 9mm but the 147 grain is above this 1125 number. We call this being supersonic and it will make a much louder sound as it breaks the sound barrier. 

Of course, there are many more kinds of cartridges and grains than what I chose to include in the table, but it is a good representation of the most common cartridges for these calibers. 

You will also notice that there is not one 45 ACP on that list that breaks 1125 feet per second. This means they are inherently subsonic(slower than the speed of sound) and will be much quieter after being suppressed. If you are using 9mm, you will have to go out of your way to find subsonic rounds.

Both of these calibers are fairly easy to suppress and many of your common pistols have aftermarket threaded barrels that are not too expensive. The most expensive part will be the suppressor itself and the tax stamp you need to have one.

Without knowing the exact specifications of the two 45 and 9mm cartridges you want to compare, it is hard to say that one will be quieter than the other assuming you use subsonic 9mm rounds. It depends on the round, suppressor, and several other variables. However, the sound is comparable for both. If you plan on suppressing a pistol, the sound should not be a deciding factor.

45 ACP vs 9mm: Home Defense and Concealed Carry

For home defense, you want something that is going to stop a threat in its tracks and not go through every wall you have. That means that the 45 ACP is going to be the better option. Of course, this is a powerful round and it is going to go through a lot, but if you are using hollow points, it will expand and transfer most of its energy on the initial impact.

It is still going to go through plenty of dry wall but will stop earlier than the 9mm. Plus it has more stopping power than the 9mm and could stop that threat sooner. Plus if you are using it as home defense, you can get a larger gun. This means higher capacity and more weight to counteract the recoil, which will make you more accurate. Putting a flashlight on the bottom of your pistol is also a good way to add weight and dissipate a  little recoil.

As for concealed carry, I rather have a 9mm. Not everyone can conceal a standard size pistol. So it is easier to conceal a slimmer 9mm that can still hold 10 plus rounds. This makes for an overall more comfortable carrying experience, without sacrificing a lot of magazine space.

9mm is also better at penetrating than 45 on average. This means that you can shoot threats through whatever concealment they may take from you. Still, the 45 may make it through, but your chances are better with the 9mm. 

Plus the 9mm has less recoil on average and is easier to control. This means that you are going to be more accurate with it while in the heat of the moment. Anyone can make a nice group while on a range, but things change when it becomes life and death. It does not matter how big or nasty your bullets are if you can not hit what you are aiming at. 9mm gives you the best chance at doing so.

9mm Current Military Use

You also can not ignore the fact that the United States military and NATO are all using the 9mm in their service pistols. The 9mm Beretta M9 became the standard service pistol of the United States in 1985 and was recently replaced by the 9mm Sig Sauer M17 in 2017.

There are quite a few reasons for this and we have already talked about many of them, so let’s look at them in a short bulleted list:

  • 9mm is cheaper to produce and buy
  • 9mm is physically lighter, and therefore easier to transport
  • Soldiers can hold more 9mm ammo at one time
  • Modern 9mm ammo has proven to be more reliable than 45 ACP
  • Soldiers are generally more accurate with 9mm
  • 9mm is able to better penetrate cover that targets hide behind

Conclusion: The 45 ACP vs 9mm debate

At the end of the day, the 9mm and 45 ACP are both great cartridges. If you want a big and slow cartridge that is able to stop targets faster, and possibly penetrate less then the 45 ACP is the way to go. On the other hand, if you want a smaller, lighter round that will penetrate more than the 9mm is the best.

The 9mm also had the advantage when it comes to recoil. It is much easier to shoot and allows users to be more accurate with it on average. The lesser recoil also prevents the user from creating a limp wrist kind of malfunction as often compared to the 45 ACP.

You will also get more rounds in your magazine when looking at a 9mm vs a 45 ACP. That can be a major bonus in most cases, but if you live in a state with magazine restrictions then this point is mute. The biggest difference is that you can have a 9mm and 45 ACP both with 10 round capacity, but the 9mm will be much smaller and easier to conceal.

Lastly, the 9mm has been the main sidearm cartridge for the United States military and NATO for nearly 40 years now. It speaks volumes for the round to be as widely used as it is in these very serious organizations. They need a round that outperforms the competition and economically makes sense, which is what they found with the 9mm.

The 45 ACP will always have its place in the firearms community and many people’s nightstands, but the 9mm has a lot of attractive talking points that are pretty hard to beat once you get out in the field or conceal carry.