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9mm vs .45 ACP: Self-Defense Caliber Showdown preview image
Oct 17 2023
7 min read

9mm vs .45 ACP: Self-Defense Caliber Showdown


9mm vs. 45 – the primary self-defense calibers for automatic pistols. One caliber, .45 ACP, won two World Wars yet has fallen out of favor, while the other caliber, 9mm Parabellum, lost two World Wars but has become the most popular handgun caliber

Ammo production handguns

How did that come to be, what are their origins, and how do they compare to one another? Keep reading to learn everything you should know about these famous handgun calibers.

Overview of .45 ACP

45 acp ammo winchester usa

History of .45 ACP

45, also known as .45 ACP (short for Automatic Colt Pistol) and 45 auto, was invented by John Moses Browning at the turn of the 20th century. Its metric equivalent is 11.43x23mm. Originally designed in 1904, it entered production in 1905 and became the primary handgun caliber of the US military until 1985, when it was replaced by the 9mm Parabellum.

The catalyst of the 45 cartridges was the Moro Insurgency of the late 1800s, a conflict in the Philippines after it was ceded to the United States in the aftermath of the Spanish-American War.

During the fighting, it was determined that current military handgun cartridges, such as the 38 Long Colt, were insufficient to guarantee stoppage. In contrast, larger caliber rounds, such as the 45 Colt revolver cartridge, were deemed more effective. Because of these combat experiences, the US authorities, who were beginning trials for a new automatic pistol, determined that the new guns must shoot a round of at least .45” diameter to be considered.

John Browning had already been developing a 41 caliber cartridge and modified it to be larger upon hearing the new Army requirements. Military acceptance tests in 1906 and 1910 between several different manufacturers saw the 45 ACP cartridges officially adopted as the standard handgun round for the military, along with Browning’s famous pistol, the Colt M1911.

There are tons of 45 pistols to choose from in today’s market, like the Glock 21 or the Sig Sauer P220.

Overview of 9mm


History of 9mm

9mm Parabellum, also known as 9mm, is even older than .45. Its origins can be traced back to the late 1800s when Georg Johann Luger designed the now-famous caliber for his namesake handgun, the Luger P08.

The 9mm Parabellum cartridge (9x19mm) traces its origins to Luger’s original cartridge, the bottlenecked 7.63×21 Parabellum, itself a derivative of the earlier 7.62×25 Borschardt cartridge, which also formed the basis of the 7.62×25 Tokarev in the Soviet Union.

The Luger P08 served in both World Wars and was eventually superseded by the Walther P38 during WWII as the primary handgun of the Wehrmacht (also chambered in 9mm Parabellum).

9mm became popular in the United States in the late 1960s when the Illinois State Police adopted the Smith & Wesson Model 39, replacing their standard .38 special revolvers. Then, in 1985, the US Army replaced the venerable M1911 with the Beretta M9, bringing the army to NATO standard, NATO using 9mm Parabellum as their primary sidearm/submachine gun caliber.

It was the introduction of the polymer-frame Glock in the early 1980’s that really put 9mm over the top from a popularity standpoint as the new designs were lighter weight than other popular metal frame 9mm pistols like the Beretta 92/M9 and CZ75 while still having a large magazine capacity.

Over the years, 9mm has become the most popular handgun caliber, with many different types of guns being chambered in this caliber.

Specification Comparison

9mm45 ACP
Bullet Diameter.355″.451″
Cartridge Length.754″.898″
Muzzle Velocity1,150fps835fps
Muzzle Energy350-400 ft⋅lbf400-500 ft⋅lbf

Key Differences: 9mm vs. 45

9mm vs 45
9mm vs .45 ACP

Physical Size

The 45 ACP cartridge is notably larger than 9mm, especially in diameter. This leads to 45 pistols having less capacity than their 9mm counterparts, or the pistols end up being unusually large. For instance, the single-stack M1911 (.45 ACP) typically has 8-round magazines, whereas its military replacement, the Beretta M9 (9mm), has 15-round magazines.

Bullet Expansion

The larger diameter of 45 means greater expansion in Jacketed Hollow Point (JHP) form. It is thought that the greater a bullet’s expansion, the greater the chance of hitting vital areas and ensuring a stoppage. Whether this is true in real life is debatable, but it is definitely a factor to consider.

Muzzle Velocity

With standard ammunition, 45 is subsonic, with a velocity around 835 ft/s. This means that if it is coupled with a silencer, the report of the gun is much quieter than 9mm, which is supersonic with standard loads, around 1,180 ft/s, and therefore harder to silence. This is why many Special Operations units prefer 45 rather than 9mm.

Cost & Affordability

When it comes to 9mm vs. 45 handguns, their base prices are broadly similar, with an advantage towards 9mm due to their prevalence and economy of scale production. Gunbroker shows a 6:1 advantage in guns available in 9mm vs. 45. More guns produced means more choices and lower prices.

9mm has a large advantage in price regarding ammunition costs. According to Ammoseek, 9mm Full Metal Jacket rounds cost 17 cents/round vs. 45 ACP at 36 cents/round, half the cost. For JHP rounds, 9mm runs as low as 32 cents/round, while 45 ACP costs 47 cents/round, two-thirds more than 9mm.

If you’re a frequent shooter, 9mm is more cost-effective.

9mm Pros & Cons

  • More pistols chambered in 9mm than 45
  • Can be more compact than 45 for the same capacity
  • Can have greater magazine capacity for the same physical size
  • Ammo is cheaper, currently half the price of 45
  • Harder to suppress (supersonic at standard velocity)
  • Less muzzle energy for high powered defensive loads
  • Less expansion with hollow point ammunition

.45 ACP Pros & Cons

  • Greater expansion with hollow point ammunition
  • Easier to suppress (subsonic at standard velocity)
  • American pedigree that appeals to the patriotic
  • More expensive ammunition than 9mm
  • Less magazine capacity than 9mm due to larger diameter
  • Harder to conceal carry due to size


Is a 45 more powerful than a 9mm?

With standard FMJ loadings, 45 and 9mm are essentially tied. A .45 with 230-grain FMJ ammunition has muzzle energy of 356 ft-lbf, while a 9mm with 115-grain FMJ ammunition has muzzle energy of 355 ft-lbf.

With higher powered defensive loads, the 45 starts pulling away, clocking in at 592 ft-lbf of muzzle energy with 185-grain +P JHP vs. 9mm firing 115 grain +P+ JHP coming in at 501 ft-lbf, an 18% advantage for 45.

Which has more recoil, 9mm or 45?

Felt recoil depends on gun size and cartridge load, so naturally, recoil varies based on several factors.

Since most 45 guns are physically large, felt recoil would be less than a compact, polymer frame 9mm pistol with standard ammunition. All bets are off with high-power defensive loads, though.

However, don’t take my word for it. Because shooting is so fun, how about stopping by your friendly neighborhood gun range and putting some lead downrange to feel for yourself?

Is 45 or 9mm better for self-defense?

Stopping power will be debated until the heat death of the universe. Some people won’t leave home without their 45ACP M1911 strapped to their side, while others like the deep concealment of a compact 9mm, or the larger magazine capacity of a wonder nine.
“Self-defense” is a broad subject, for sure. Because there are a larger variety of guns chambered in 9mm, along with a greater variety and lower price of defensive loads in 9mm vs 45, I would give the edge to 9mm.

Still, I’m going to assume that you, dear reader, aren’t Butch Cassidy. You’re not trying to fight the Bolivian army, so if it just feels plain un-American to leave home without John Browning’s crowning handgun achievement in your holster, along with 8+1 rounds of your favorite hollow points, I won’t judge you a single bit.

The most important aspect of self-defense is putting rounds on target, so whatever caliber you choose, practice often, not only for accuracy’s sake but to ensure that your carry piece is reliable. You want to make sure it goes BANG when you pull the trigger and that the projectile hits what you intend to hit. Your life, and the lives of others around you, depend on it.


Both 9mm and .45 ACP are adequate self-defense calibers and have a long historical pedigree. However, since the 1980s, the popularity of 9mm has exploded, leading to greater choices in pistols vs. 45, along with dramatically lower ammunition prices.

These days, buying a 45 ACP pistol is more of an emotional choice, but it’s hard to say it’s a wrong choice unless money is a factor. No matter which caliber you choose, no doubt you’ll have fun shooting it.

Written by Joel Nordness
Joel Nordness photo Joel grew up in the cornfields of Illinois. After college, he had a brief stint in California, befriending veterans at the Navy base he worked at who introduced him to shooting. Realizing how much fun shooting could be, he carried that passion with him to his new home in Indiana, where he developed a love for rare and unusual handguns and firearm history. He tries his best to keep his gun collection to reasonable levels while doing what he can to introduce new shooters to the joy of the hobby.


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