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What is the Caliber of the 9 MM?-A Complete Dependable Guide

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What Caliber is the 9 mm? 

The short answer is that the caliber of a 9 mm is 9 mm….yes that is right. 9 mm is actually the designation of the caliber. However, it has shocked us here at Outdoor Methods that many gun owners are excellent marksman, but still do not know what caliber really means or how it is designated. Let us take a systemic approach and explain what is the caliber of the 9 mm below.


How is a Caliber Determined? 

Caliber, in simple terms, is a designation assigned to a specific group of guns and cartridges. This designation is determined by one of two methods. The first method designates a caliber using the dimension of a guns’ barrel. An example of a caliber assigned using is this method is the British .303. The second method identifies a caliber by the width of the bullet, not the round.

An excellent example of this method is the 9 mm, which was designated measuring the bullet width that is .355 inches or 9.017 mm. So we know a 9 mm is a 9 mm caliber, and we understand how calibers are determined Great! That was easy. However, why would somebody want to use such a small caliber? 

What Makes People like the 9 mm 

  • You get a decent amount of power from a smaller round. As a result, you get less recoil when shooting
  • Smaller guns can be made due to the relatively small size of the cartridge which is better for concealment 
  • The 9 mm is one of the most abundant rounds in the world, making it reasonably cheap to make, and therefore reasonably cheap to buy. 
  • Due to an improvement in bullet design, some 9 mm cartridges outperform the .40 and .45 rounds. 
  • It is the default NATO round.

However, the 9 mm caliber has really started to become popular over the past few years because the FBI has switched to it being their default caliber for several reasons. Some of these reasons are 9 mm firearms have a cheaper operational cost compared to larger calibers, and studies show that FBI agents are more accurate with it compared to larger calibers.

9 mm for Conceal Carry 

Many old school gun enthusiasts will tell you that the 9mm does not have enough knockdown power. However, as the FBI puts it, knockdown power is a myth, and there is no data to back up the term knockdown power. The 9mm magazine can generally hold more rounds than most .40 and .45 in a smaller frame gun. This will allow you to be able to conceal your weapon easier without giving up the number of shots that you can carry while not giving up concealment.

Lastly, since many people will only practice with their conceal carry weapons a few times (if at all), a gun with less recoil will be more manageable for them to handle and, in theory, will mean they will be more accurate. While we do not want you to use this as an excuse not to practice if life gets in the way where you cannot find time to shoot more than a few times a year, less recoil will be very helpful in allowing you to defend yourself if the time ever comes. 


What is the caliber of the 9 mm? Well hate to break it to you, but it is 9 mm, and while the old school train of thought was that the 9 mm is an underpowered caliber, data from the last few decades shows otherwise. 9 mm cartridges have been so heavily re-engineered that they hit above their weight class by outperforming some larger calibers. As for 9 mm pistols, they can be designed to be smaller than most guns while still being able to carry 10-15 rounds in a magazine. So next time you hear somebody talking down about the 9 mm, you can now educate them on why this is not a caliber to be laughed at. 

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