Posted On October 25, 2013 by Print This Post

Accuracy Matters: Calibers, Cartridges and Kindles by Adam Firestone

Since I met ADAM FIRESTONE last year, I’ve come to realize how much I don’t know about weapons. (Hint: It’s a lot.) Take calibers, for instance. I’m pretty sure Dirty Harry’s gun was a .44 Magnum, and I think Saturday Night Specials are .22s, but that’s the extent of my questionable knowledge. Luckily, when I draw a blank (figuratively speaking), I know Adam will have the answers. Need help separating calibers from cartridges and other bullet-y things? (Sorry, Adam.) Read on!


On Tuesday, I committed one of the business traveler’s cardinal sins. Egregiously, I might add. As atonement, this month’s column will discuss caliber designations, their rationales and meanings. But enough of that for now. Let’s get back to the much more embarrassing public expiation of my sins…

Specifically, I managed to leave my Amazon Kindle at home as I was driven off to the airport. For those of you unfamiliar with the sensation, there’s a flash of exquisite panic followed almost immediately by a monumental sense of anger and loathing directed at oneself. After a few minutes spent wallowing in the fury bath an overwhelming surge of “What the @!!$?% am I gonna do NOW?”

The answer is pretty mundane. You wander into the airport bookshop and shell out an inordinate amount of money for a book and a magazine that, but for the dire circumstances, you’d not have purchased in the first place. In my case, the lucky purchase was Robert B. Parker’s Fool Me Twice, A Jesse Stone Novel by Michael Brandman. As far as airborne brain gum goes, it’s a nice little book. The plotlines are interesting and not difficult to follow, the characters are engaging and the VBGs come to a suitably appropriate end. I enjoyed it.


Actually, that’s not quite true. I *was* enjoying it until the Mr. Brandman displayed an appalling lack of knowledge about firearms and caliber designations that left me cold. And, while I might be a bit of a Type A, detail-oriented, firearms techno-geek, the reality is that an author’s failure to pay attention to detail turns off readers and makes them less likely to come back.

That being said, let me provide a couple of examples of the gaffes that turned me off:

a. In one case, an antagonist threatens the hero with a “.38-Caliber Beretta pistol.” That’s great, except for the fact that you can pore through Beretta catalogues for the last hundred years and not find anything labeled as “.38 caliber.” The problem is only exacerbated when one realizes that there are probably over twenty different cartridges that can, at least dimensionally, be referred to as “.38 caliber cartridges.”

b. In another case, the VBG gets the drop on the hero and threatens him with a “.45-millimeter Ruger pistol.” Read that again. Point forty-five. Millimeters. That’s the size of half a mustard seed. Or maybe a smallish grain of sand. Well that’s intimidating. NOT. Stop or I’ll dust you to death? Cease and desist or face the condiments? Ruger’s suddenly making self-spicing hot dog machines? Whiskey tango foxtrot, over? I suspect Mr. Brandman was referring to a .45 *CALIBER* Ruger pistol. However, the net effect of the misstatement was to derail the scene and disrupt the credibility of both the author and the book.

So let’s talk a little bit about guns, calibers and the apparently little known fact that words mean things.

What’s a Caliber?

A caliber is, in the end, just a measurement. It measures either:

• The approximate internal diameter of the barrel; or
• The diameter of the projectile it fires.
In a rifled barrel, diameter is measured between opposing lands or grooves; groove measurements are common in cartridge designations originating in the United States, while land measurements are more common in Europe. RiflingXC The distinction is largely academic at this point. For purposes of writing, it’s important to remember that caliber (more or less) equals the diameter of the projectile, and that the measurement’s popular use identifies both firearms and their ammunition. For example, a “.45” is a pistol that fires .45 caliber ammunition.

Additionally, caliber can be expressed in either the metric system or the English system. In the metric system, calibers are expressed as decimal or integer millimeters, such as 9mm or 7.65mm. In the English system, caliber is expressed as a decimal fraction of an inch. This is usually expressed in hundredths of an inch, but may also be shown in thousandths. Accordingly, a .45 caliber handgun fires a projectile that is nominally 45/100 of an inch in diameter. Alternately, a .357 Magnum uses a projectile that is 357/1000 of an inch in diameter.

That’s only part of the issue, however. In popular language, “caliber” has come to be interchangeable with “cartridge.” Cartridge refers to the overall assembly of projectile, propellant, primer and case that constitutes a round of ammunition. A cartridge’s external dimensions are tightly controlled so as to ensure that it will fit into and function with a firearm that is properly chambered for that particular cartridge. Key among these dimensions is the cartridge case length. After all, if the case is too long, the cartridge just won’t fit into the firearm. As a result, many cartridges, especially metric ones, are given a nomenclature that describes both bullet diameter and case length. So, the standard 9mm cartridge used by NATO forces is the “9x19mm,” indicating a bullet diameter of 9mm and a case length of 19mm.


In a smoothbore barrel, such as that found on a shotgun, caliber is referred to as “gauge.” Gauge refers to the number of lead balls with a diameter equivalent to that of the barrel that it would take to weigh one pound. For example, a 12 gauge shotgun has a bore diameter of 0.729”. A spherical lead ball of 0.729” in diameter weighs 1/12 of a pound, hence the nomenclature “12 gauge.” However, as with metric cartridges, the length of a shotgun shell is a critical dimension. As a result, one will often see shotgun shells described in terms of both gauge and shell length, such as ‘12 gauge, 2 ¾”’ or ’12 gauge, 3”’.

They Have Given You a Number and Taken Away Your Name

Now that we have an understanding of the basic dimensional naming conventions, let’s take a hard left into the really hard parts. Specifically, colloquial, proprietary and redundant naming.

Often, a cartridge will be produced by many manufacturers, and each one will give it a discrete proprietary name. Muddying the waters further, when governments adopt a particular cartridge for military organizations, they add their own “official” nomenclature. To illustrate the point, here’s a pop quiz. What’s the difference between the following cartridges:

• 9x19mm
• Pistolenpatrone 08
• 9mm Luger
• 9mm Parabellum
• 9mm NATO

Answer: There is none. They all refer to the same 9x19mm cartridge developed by Georg Luger in 1901 and brought to market by Deutsche Waffen- und Munitionsfabriken (DWM) in 1902.

Conversely, there are many cartridges that fire bullets of similar diameter, but that are dimensionally dissimilar and not at all interchangeable. The following cartridges all use bullets that are nominally .38 caliber, but are completely distinct:

• .38 S&W
• .38 Long Colt
• .38 Short Colt
• .38 Special
• .38 Super Automatic
• .38 ACP
• .38-40 Winchester
• .380 ACP
• .38 Supercomp
• .38 Super Lapua
• .38 TJ (.38 Todd Jarrett)

(In fairness, the .38 Super, Supercomp, Super Lapua and TJ are all based on the .38 ACP case and are dimensionally similar.) It gets more interesting, however. In many cases, the nominal dimension (e.g., .38”) isn’t accurate. The actual bullet dimension of the .38 Special cartridge is between .357” and .358”. Similarly, the bullet diameter of the .44 Magnum is .429”.

These misleading names are maintained for either obscure techno-historical reasons or, in many cases, because marketing departments felt the name would resonate more effectively with buyers. Think about it. Clint Eastwood gritting out “This is a Four Twenty Nine Magnum, the most powerful handgun in the world…” just wouldn’t have the same effect!

When it comes to rifle cartridges, all bets are off. Some are named based on the projectile diameter and the amount of propellant (measured in grains), such as the .45-70, the .30-40 Krag or the .30-30 Winchester. Others are named based on the year of adoption, such as the .30-06 (.30 caliber cartridge adopted in 1906). Others are named based on the bore diameter of the rifle rather than the actual diameter of the bullet. For example, the .303 British cartridge (the mainstay of the British Army for almost 70 years) has a bullet diameter of between .311” and .312”. And then there are those for which names were invented by distributors: The Soviet M43 7.62x39mm cartridge was, for a number of years, referred to as the “7.62mm Soviet” on the American commercial market.

Summing It Up


There’s a lot to know, and concomitantly, a lot of mistakes that can be made by the unwary author when it comes to calibers and cartridges. Fortunately, there are some quick and dirty rules of thumb that can be employed to keep out of trouble:

• When you’re talking about a 9mm handgun, the gun itself is almost always going to be a semiautomatic pistol and the cartridge it fires will be the 9mm Parabellum (or 9x19mm or 9mm Luger or . . . )
• When you’re talking about a .45, it’s always going to be .45 caliber. NEVER millimeters. Moreover, unless you’re writing a western, it’s likely that it’s a semiautomatic pistol firing a .45 ACP cartridge.
• .38 typically refers to the .38 Special cartridge, which is usually fired from revolvers.
• .32 can be either the .32 ACP, a small semiauto cartridge, or the .32-20 revolver cartridge.

In the end, accurately portraying caliber comes down to the eternal truth: Words mean things.

Happy writing!


Have questions for Adam? Don’t be shy!

MICHELLE MCLEAN joins us on Monday.


Bio: Adam Firestone brings more than 25 years of experience with weapon systems including small arms, artillery, armor, area denial systems and precision guided munitions to Romance University. Additionally, Adam is an accomplished small arms instructor, editor, literary consultant and co-author of a recently published work on the production of rifles in the United States for Allied forces during the First World War.

Adam has been providing general and technical editing services to authors and publishing houses specializing in firearms books since the early 2000s. Additionally, Adam provides literary consulting services to fiction authors including action scene choreography, technical vetting and technical editing. In this line of experience, Adam has had the fortune to work with well known authors including Shannon McKenna and Elizabeth Jennings.

Check out Adam’s blog here:

Calling all program directors! Looking for a workshop participants won’t soon forget? Contact Adam Firestone to check his availability for conferences and chapter meetings. (He’d love to do a workshop at RWA National.) The all-day workshop he did for the Ohio Valley RWA chapter was fabulous!

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13 Responses to “Accuracy Matters: Calibers, Cartridges and Kindles by Adam Firestone”

  1. Morning Adam!

    Well I am personally glad you forgot your Kindle if it inspired you to write this post! =) But I’m most grateful for the quick and dirty rules.

    I do remember once picking up shotgun shells for my dad, and he’d told me to get something like the 12 gauge 2 3/4″ ones. I came home with the 12 gauge 3″ and couldn’t understand why he was mad – it’s just a bit longer! won’t they go faster that way??? lol….ooops.

    Great post again and definitely a keeper!


    Posted by Carrie Spencer | October 25, 2013, 8:07 am
  2. Good morning, Adam. Thank you for all of this great info!

    I went to a shooting range with a friend last year and he gave me different sized handguns to try. I was amazed at the differences in all the weapons. Not just the size of them, but the grips and how they felt in my hand. It was a good lesson in the details.

    Thanks for being here.

    Posted by Adrienne Giordano | October 25, 2013, 8:10 am
  3. Amazing as always, Adam!

    Posted by Lori Schafer | October 25, 2013, 8:26 am
  4. Hi Adam – I’m sure you’ll bang your head on the desk when I ask this, but are bullets, etc. called weapon “accessories?” That sounds kind of, dare I say, girlie, but I can’t think of a better word. Then again, no caffeine yet today so I’m not, um, firing on all cylinders! (Is that accurate word usage?)

    Posted by Becke Martin Davis | October 25, 2013, 9:28 am
    • There are accessories – but they are usually things like slings, cases, cleaning supplies and tools.

      PS – I know that by “bullets” you meant ONLY the projectiles, not loaded ammunition, right?

      Posted by Adam Firestone | October 25, 2013, 8:34 pm
      • Yes! Although I do need to dig out my notes from the OVRWA workshop. I took TONS of notes, but then I had to go and move. I know I have the notes, I just haven’t figured out exactly WHERE I have them. I remember you going over this, but I’ll remember it better when my notes are in front of me!

        Posted by Becke Martin Davis | October 26, 2013, 12:19 am
  5. Hi Adam,

    Your posts are so interesting. If you put a smaller caliber bullet in a revolver, will the gun still fire?

    Posted by Jennifer Tanner | October 25, 2013, 8:14 pm
    • Smaller caliber bullet or smaller caliber CARTRIDGE?

      The answer is “it depends.” There are some smaller caliber cartridges that might gain enough purchase on a revolver’s cylinder to let the firing pin detonate a primer, but the bullet would, if it went anywhere, would rattle down the barrel and where it went would be anyone’s guess.

      Posted by Adam Firestone | October 25, 2013, 8:41 pm
  6. For some reason I started thinking about silver bullets while reading the comments. Would silver bullets work the same as regular bullets? Does the type of metal make a difference?

    Posted by Becke Martin Davis | October 26, 2013, 12:21 am
  7. Adam- Thanks for another informative and thought-provoking post!

    Posted by Becke Martin Davis | October 26, 2013, 12:22 am

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