Ballistics 101: What Is Caliber, Exactly?

“Caliber”. It can mean a lot of different things, but when we use it, what does it really mean, and what’s its significance?

Title image: From left to right are the 7.65 Parabellum, 7.63 Mauser, .300 Blackout, 7.62×45 Czech, .30 Remington, 7.62 NATO, .300 WSM, 7.5×55 Swiss, and .30-06 M2 AP. All of these cartridges are the same caliber (they all use .308 caliber bullets), but paradoxically they are all also different calibers (they aren’t interchangeable with one another).

Today I begin a series of posts on basic ballistics, and the theory behind them, both external (how a bullet flies through the air) and terminal (how a bullet penetrates a target). For the first few installments, we’ll be exploring some very introductory subjects, but hopefully with enough depth that even those readers already familiar will get something out of it, still. As you have already realized, this first episode will deal with the history and usage of the word “caliber”.


1 : the diameter of a round or cylindrical body

e.g. : What caliber is this cleaning rod?

Caliber is perhaps one of the oldest words in the firearms lexicon. It goes all the way back to the Greek καλαπουσ (kalapous), referring to the hard wooden objects used by shoemakers to mold leather into shoes. At some point, it seems, this term was applied by way of analogy to bullet molds, likely initially with regards to lead sling bullets. As the firearm was developed, this term made its way through Arabic, Tuscan, Middle French, and then Early Modern English, to become the modern day word caliber, which now means many things from “quality” to “measurement”. As a sidenote, the word caliper, referring to a tool used to measure span, seems to be a derivative of the firearms-related word caliber.


2 : the diameter of a bore of a gun

e.g. : A .50 caliber barrel has a mighty big hole at the end.

With regards to modern firearms, the word “caliber” carries with it a couple of important qualities that today are distinct and can cause confusion, but which stem from a relatively recent change in the fundamental nature of small arms technology. Before the 1850s, almost all firearms were of the muzzle-loading type, and virtually all firearms fired round lead balls. These round balls scaled in weight according to a cube function with their size, given a certain lead alloy used to cast them. This meant that, roughly, a bullet for a firearm that was 0.50″ (12.7mm) in diameter always had the same weight as any other bullet with the same diameter, and the same was true for a bullet 0.70″ (17.8mm), or for any bullet of any other respective diameter. All of these projectiles were, as well, equally compatible with all firearms of the corresponding bore diameter, and – although propellant charges could be adjusted to a certain degree – all firearms with a given bore diameter had the same capabilities in terms of range and terminal performance as any other of that same bore.


3 : the diameter of a bullet or other projectile

e.g. : I can load .30 caliber bullets in a .308 Winchester case, right?

What this means is that for hundreds of years, from the 12th Century to the mid 19th Century, the word “caliber” at once summed up both the interchangeability of ammunition with a firearm that could fire it, and the capability of that firearm-ammunition combination. A .65 caliber rifle was, at one time, virtually always more capable than a .50 caliber rifle, which was in term more capable than a .45 caliber rifle, and so on, and further each caliber of weapon could use any ammunition of that caliber, as well.


4 : the type of ammunition compatible with a certain firearm

e.g. : This is a 7.62x54mmR caliber round.

However, in the mid-19th Century, things changed. In the first half of the century, the oblong bullet (incarnated chiefly in the legendary Minié ball projectile) was perfected, disconnecting the weight of the projectile from its caliber. Now, different bullets in the same caliber could have a wide variety of different weights, depending on their exact shape. Soon after, the self-contained metallic cartridge was also invented, which resulted in a more fixed propellant charge for individual ammunition, and further differentiating the capabilities and interchangeability of different weapons and ammunition with the same nominal “caliber” of bore or bullet.


5 : the type of firearm compatible with a certain kind of ammunition

e.g. : The Mosin Nagant is in 7.62x54mmR caliber.

Further innovations, like smokeless powder, spitzer bullets, and others created an even wider set of possible ammunition paradigms, which continue to expand to this day. This variety has fragmented the meaning of the word “caliber” along with it, resulting in the five different definitions given in this article. As a result, other terms have popped up to differentiate these concepts, such as “bullet diameter” to mean (3), or “chambering” to mean (5), but “caliber” remains an extremely common choice of word for all five meanings.

So “caliber” has gone from meaning the mold used to create a bullet, to a system of nomenclature indicating imprecisely both the capabilities and the interchangeability (or lack thereof) of different kinds of ammunition, and the weapons that fire them. Indeed, now, the word “caliber” more often refers to the name of a given cartridge-rifle system than it does any physical quality of either, for example the .223 Remington caliber is not named after any specific measurement on the bullet (0.224″), case, or bore (0.219″), but simply so-named to differentiate it from other similarly-named calibers!

Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at


  • Good, I think people will dig this.

  • Anonymoose

    I would take a rifled .45 or .50 over a smooth .65 any day, though.

    • bull

      frontstuffer? it depends… a rifled .50 with minie balls .. sure. but if you only have round balls and need rate of fire , smoothbores are better. thats why they remained for so damn long.

      • Marcus D.

        This is true. The rifles fouled much faster, the benefits being greater range and accuracy than a musket. However, the reason smooth bores stuck around was two-fold: they were easier to manufacture, and therefore less expensive, and they could fire buck or ball.

    • Austin

      Why not 4 bore?

      • Anonymoose

        Why not 2 bore?

        • iksnilol

          Why not 1 bore ?

          I mean, those 2 and 4 bore guns must be heavy to carry with all those bores.

          • lucusloc

            boooo. I may be a new father, but if I ever get that bad shoot me 😉

          • iksnilol

            I’ma do it with the 1 bore since I am tired and don’t want to bother with the 4 or goodness forbid 8 bore.

        • Norm Glitz

          Shoulder fired? That could leave a mark!

    • Major Tom

      I’d take a rifle chambered in .44-40 (like some of the Winchester lever actions) over an old .45 or .50 rifled musket.

      • Anonymoose

        Yeah, but we’re just talking about muzzleloaders here. Also, I have heard many times that the .44-40 used to be a lot more powerful (there was a carbine-specific loading) than it is today.

  • politicsbyothermeans

    Great article, Nathaniel. It’s interesting that some calibers are part and parcel of our own lexicon. Five five six and thirty ought six mean something to most of our readers. Boutique rounds sometimes end up with a qualifier. I can’t just say that I have a six point five rifle without mentioning that it is a Grendel.

    • gunsandrockets

      Most cartridge nomenclature has some basic logic (even when distorted by marketing hype) as in the cartridges you mentioned.

      But can anyone explain to me the logic of .25-45 Sharps? Which mixes up english and metric units of measurement?

      • randomswede

        With “Sharps” in the name I thought for sure it was a cartridge aged like the .30-30, .30 caliber with 30 grains of blackpowder behind it.

        For those who don’t feel like looking it up; it’s .223 Remington necked to 6.5mm very similar to the 6.5 MPC and along the lines of .300 Blackout.

        • It’s necked up to 6.35mm (.257), not 6.5mm (.264).

          • randomswede

            My apologies, I trusted Wikipedia.

          • FWIW: Wiki listed the correct diameter of the projectile, but in this case, the cartridge designation is based upon the diameter of the bore.

          • Marcus D.

            Another point of confusion that the article points out: the cartridge designation is essentially meaningless, since one can never know whether the designation refers to projectile diameter or bore diameter.

          • Exactly, and given the nature of marketing, sometimes commercial cartridge designations are completely unrelated to either the bore or projectile diameter. For example, you can find designations for cartridges using 0.224″ projectiles ranging from the .218 Bee to the .225 Winchester. And then there are the odd naming conventions that resulted in the .38 Special (~0.357″), .38-40 (~0.400″), and .44 Special (~0.429″).

          • Marcus D.

            To be fair, the .38 Special derived from the original cartridge conversions for the .36 caliber percussion pistols. The round ball for the .36 starts at .375 (rounded up to .38) before loading, and the first cartridges (the .38 Short Colt) used the same diameter bullet because the Richards-Mason conversion saved the cylinder, removing the back end and replacing it with a tappet system. It was later iterations that replaced the heeled .38 Short Colt bullet with a smaller diameter projectile that was closer in size to the bore diameter (.357).

          • True, but it is confusing for the new and/or casual shooter.

          • Marcus D.

            Not according the the conversion program on my calculator, which places .257 at a 6.5278 mm. The same calculator says that .250 converts to 6.35, and .264 to 6.7 mm. I think Mr. Watters, just below, explains the confusion.

          • You are confusing bore and groove diameter.

            The metric designations are bore diameters, and the inch designations in parentheses are bullet diameters.

            That’s just the nomenclature conventions for those systems. I didn’t choose ’em.

        • lucusloc

          I would have made the same assumption. Mixing metric and imperial measurements into one definition is just wrong on so many levels.

          • randomswede

            Especially using the same “verse meter” as the turn-of-the-century cartridges.

      • FWIW: IMI had done it with early lots of the .41 Action Express. Labels read .41×22.

      • Marcus D.

        What is the metric measurement? My understanding that the caliber of the bullet (or barrel, this changed a lot at that point in history) was .25, and the 45 referred to the grains of black powder behind the bullet. Same with the .45-70.

        • iksnilol

          45 is the metric measurement.

          It is a 5.56×45 necked up to 6.35 or something. So the .25 refers to the caliber whilst the “-45” refers to the 45mm case length IIRC.

          • Marcus D.

            Ah, I see, I assumed it was an old loading, not a new one. During the black powder era, the second number usually referred to the grains of powder (one exception being the .38-40 WCF, which actually fires a .40 caliber bullet). My handy dandy converter says that the .257 bullet is a 6.5mm. So you are correct: to be consistent, the Sharps should be a 6.5 x 45.

        • HollowTs

          True but, unless you know the particular history of a cartridge it can be very confusing. E.G. .30-06 is a thirty caliber round. However the 06 denotes the year it was created 1906. It seems today we use the second number designation mainly for case size.

  • Hudson

    In some contexts, e.g. guns aboard a warship, “caliber” is used to
    describe the barrel length as multiples of the bore diameter. A “5-inch
    50 caliber” gun has a bore diameter of 5 in (12.7 cm) and a barrel
    length of 50 times 5 in = 250 in (6.35 m). (quoted from Wikipedia)

    • Guest

      And to expand on the above comment, we also use “calibers” as a measurement in creating bullets. Since the measurement of a “caliber” changes with the actual size of the bore, we can safely say that a tangent ogive bullet has an 8 caliber radius ogive or a secant bullet has a 16 caliber radius ogive. It allows our measurements to go up and down proportionally.

    • lucusloc

      I’m not sure this is correct, but I though in big gun terminology when referring to length, the word “caliber” was pluralized? e.g. “5-inch 50 calibers”. I’m not sure Wikipedia would document a nuance such as that accurately. I would be interested to hear from someone who designs big guns (they are usually the most knowledgeable people about terminology in their particular field).

      • ostiariusalpha

        I don’t design cannons, but one of my in-laws was an lieutenant of an artillery unit. The “caliber” in cases like this refers to the bore diameter as a unit of measure; the 5″ bore gets multiplied x50 to give a bore length of 250″/20’10″/635cm. Samantha J also mentioned this use.

        • lucusloc

          Yes, but that just reinforces my suspicion that it is supposed to be pluralized in that context. “5 inch, 50 calibers” and the “long” at the end is implied. Again, I’m obviously not an expert on the matter, but I think pluralized is correct and it just gets dropped in the common vernacular? Though given the use case it would be hard to argue any information is lost, so probably not worth spending any more time on.

          In definition 5 of the article, however, information is definitely lost, so I think it should be dropped a misinformation.

    • Georgiaboy61

      As recently as the Second World War, that system was also used in the nomenclature of the tank cannon. I don’t know if it is still in use today or not; perhaps some present-day tankers can comment on that.

  • Gary OlsenSaville

    Correct me if I’m mistaken, but isnt internal ballistics the study of what the projectile does while it’s in the firearm. And the study of what the bullet does inside its target is terminal ballistics.

    • Katie A

      You are correct. External ballistics covers projectiles in flight without benefit of propulsion (so, after leaving the barrel) while internal covers projectiles within a firearm. Terminal ballistics has to do with impact and the transfer of kinectic energy. Yeah I just repeated what you said, basically…so yes, I agree. You’re right.

    • A

      Yeah, you’re right. This guy makes so many mistakes in his posts about ballistics I’ve stopped taking him seriously. I’d like to know what his credentials are since he likes to act like an expert so often.

      • Everybody makes mistakes, I do my best to correct mine when they’re found. That’s all I can do.

        • 5200

          Well said.

      • Bronezhilet

        Mind proving him wrong?

      • Of course his credentials matter! A Delta operator with no college degree in fluid dynamics and physics would the the superior person to challenge @nathaniel_f:disqus Army Research Labs supported statements right?

      • Rollin Shultz

        Publishers are always looking for a good blogger to write on such subjects, I can’t wait to see yours. Feel free to submit an article and link it back to this discussion, I am sure many of us are curious to see you man up.

      • Mike Lashewitz

        And here I am thinking Nathaniel is the creator and financier of, The Firearm Blog. Which makes him the guy who decided to take his own time to start this and do the most of the work.
        Personally I applaud Nathaniel BECAUSE I have witnessed him accepting corrections and telling the group about those mistakes like an adult. He has readily admitted he does not “know it all”. I don’t think anybody does. Do you?
        What I find odd is how you say “this guy” as if it is some sort of negative thing. After all you are “that guy” who specifically pointed it out in the way you did. Not mature at all…
        I have a great idea, how about you starting your own firearm blog? Then we will have another source for information. I realize that there are costs involved. Those costs may be prohibitive. I should know because i operate 5 blogs myself on entirely different subjects having nothing to do with firearms.
        You know blogs on subjects like prepping, bee keeping, spirituality vs religion, natural medicine/plant identification, quantum physics and how to operate video cameras.
        However I also believe that Nathan also accepts blogs from most anyone who submits them. Pretty much as long as it stays on topic and is well researched with supporting sources.
        But I could be wrong on that…

        • Hi Mike,

          Nope, I am not the creator. Just a writer. Steve Johnson is the creator of TFB.

          • Mike Lashewitz

            Well Nathan you seem to be doing a pretty good job!

          • Hey, thanks, Mike!

    • Whoooopsie, that’s an embarrassing typo. You are correct sir!

    • Bronezhilet

      I would actually say that terminal ballistics is what the projectile does to whatever it hits. You don’t always penetrate the target and, I know it might sound a bit silly, but you don’t always hit what you intend to hit.

      But hey, semantics, I guess.

  • Armand Fight

    Great article…thanks!

  • Vitor Roma

    6.5 is the magic number that answers everything, forget about 42. It is known.

  • Vitor Roma

    The 7.62×45 Czech looks so nice we could call it 7.62×45 Sexy.

  • Bradley

    In diameter measurement a caliber is .01″ Your article is interesting, but it is written from the perspective of using the term incorrectly. Sure plenty of people will say .223 remington is the caliber, but that doesn’t make it correct. In fact with the complexity and variety of projectiles and cartridges today caliber has become pretty much useless as a form of measurement.

    • Caliber is not, nor so far as I know has ever been, a unit of measure.

      • Wolfgar

        It is when talking about a person 🙂

        • You would say “Bob is a great guy, he is fifteen calibers”?

          • Wolfgar

            No, you would say Bob is a great guy of high caliber or you would say Bob is not a great guy and of low caliber if you are Bob’s ex-wife.

          • iksnilol

            I know Bob, he is at best 4 calibers.

            At worst, like not even a half a caliber.

      • ostiariusalpha

        Actually, caliber is used as an Imperial unit of specifically .01″, and has been so for over 150 years.

        • In what localities? I mean, I wouldn’t put it past some areas of the Commonwealth, but I’ve never ever seen it used as a unit in the US (outside of its traditional Naval application, but it’s not a fixed unit there).

          And, actually, I asked a British friend of mine about it after Bradley made his comment, and he’d never heard of it being used as a unit of measure either. Regardless, so many people use it “wrong” (as in, not as a unit), that it’s hard to take issue with it except very semantically.

          • somethingclever

            I found this entry for caliber in the OED “1778 Philos. Trans. 1777 (Royal Soc.) 68 65 The bore..was nearly 20½ calibers long.” It’s not listed as a separate meaning. I’d agree, though that it can’t be very regular in English if it doesn’t have its own entry in the OED.

          • Right, but that’s used in the sense of “the length of the bore was 20.5 bore diameters long”, obviously. That usage is still around today for large artillery, but it’s not a true unit of measure.

      • Bradley

        Merriam webster Full Definition of caliber
        a : degree of mental capacity or moral quality
        b : degree of excellence or importance
        a : the diameter of a bullet or other projectile
        b : the diameter of a bore of a gun usually expressed in hundredths or thousandths of an inch and typically written as a decimal fraction
        : the diameter of a round or cylindrical body; especially : the internal diameter of a hollow cylinder

        I can see your point about common usage, but I still think almost anyone knows that 50 caliber in general would mean .50″. Gauge has a lot of usages too, but for shotguns it is a bore measurement. It is a measure of how many lead balls the size of the bore would weigh a pound. I still have to disagree. It would make an interesting subject for some historical research though.

        • Bradley,

          The unit of measure is hundredths (or thousandths) of an inch, not “caliber”. “Caliber” just tells you what you’re measuring.

  • Samantha J

    If you consider artillery to be firearms… the word “caliber” also refers to the length of the tube in multiples of the bore diameter.

    • Jonathan Ferguson

      1) I don’t, because they aren’t.
      2) That term has a name, and it’s ‘calibre lengths’. The definition of calibre remains the diameter of a bore or a bullet.

      • I’ve wondered about that. They’re not “firearms” because they aren’t really “arms”.

        So they’re… By analogy, I guess, “fire engines”?

        I guess that term is taken, though!

        • Jonathan Ferguson

          That’s the rationale I think. Although some medievalists refer to early guns collectively as “firearms”. It’s a relatively modern term though, & I’m fairly sure the word artillery had come to mean “big guns” by the time “firearm” was popular for a handheld gun.

  • Audie Bakerson

    Now what comes to mind first when someone says “7.62”?

    • mechamaster

      NATO oriented : 7,62x51mm
      Warsaw Pact oriented : 7,62x39mm, and 7,62x54R mm

      • Audie Bakerson

        No love for the Nagant revolver or TT-33?

        • ostiariusalpha

          None. ?

          • KestrelBike


        • mechamaster

          Well, for modern user, two of the most popular Russian caliber in 7,62 is 7,62x39mm, and 7,62x54R mm, that always ring a bell first and 2nd.

          The 7,62 Tokarev is the 3rd, and Nagant 7.62×38mmR is the 4th. ^_^

          ( oh, sometimes the .30-06 / 7,62x63mm is ring a bell too for US Oriented )

    • lucusloc

      My next though is “yes, but what is the actual cartridge?”

    • iksnilol

      A fun game?

    • HollowTs

      7.62 Nato. Then 7.62×39. For me they are the most common uses for that nomenclature in the U.S. I have a military background though. So that may be the reason I go there first.

  • lucusloc

    Maybe it is just the crew I run with, but I never see “caliber” used for #5. The Nagant chambers the 7.62x54R *cartridge*. If you do not care about the exact cartridge you could ask what caliber the gun is, but at that point most people I know would only respond with the relevant dimension, not the full cartridge name. This is not out of pedantry or dickishness, but out of the assumption that you want the diameter of the round in a more familiar number. If you asked me, here at my local range, what caliber my Nagant is, I will tell you “30”, not 7.62.

    Now this is the point where I do get a bit pedantic, because I believe words mean things and we should strive to keep those meaning sharp and accurate. With regards to firearms, caliber exclusively refers to the diameter of the bore or projectile, nothing else. Using it in any other way is a faux pas equivalent to calling a magazine a “clip”. The usage should be gently corrected, and the reason for the correction made clear. If well allow the common usage to slip then meaning is lost, and it take fare more words than necessary to convey accurate information. Keeping the definitions of words distinct means more information can be conveyed in less time and with less confusion.

    • Julio

      My feelings exactly. To add “calibre” to the name of a cartridge is unnecessary and imprecise.

    • Michael Lubrecht

      Yep – I’ve never, nor have the folks I’ve taken instruction from or taught, ever really equated “caliber” with “cartridge.” If a buddy is showing off a new rifle, he might be asked, “So, what round do you shoot in that thing?” Or, “Is that a .308?” [implying .308 Winchester]. But caliber is seldom substituted for cartridge, unless the round is ubiquitous – for example, “Hey is that AR you’re shooting a 5.56, or a 6.5?” Again, implying the ’45’ or ‘Grendel.’ But, nobody I know of will say, “Hey, that .300 Ultra Mag caliber you have kicks like a mule!!”

      • lucusloc

        Yeah, if I am in a room with a bunch of enthusiasts we will use *the caliber* as shorthand for *the cartridge*, dropping the other dimension. But that doesn’t of mean we change the definition of the word. If we were being lazy but still wanted to be clear we would say “5.56 cartridge” and just drop the “x45” part. We would never say “5.56 caliber” unless we were explicitly talking about the diameter of the bullet or the bore. And that caliber-only shorthand works only in platforms with only one common cartridge in that caliber. The number of “only”s in that sentence tells you how limited in scope that shorthand is. If you had some random bolt action and I asked what it shot, and you replied with “30” (or even “30 caliber”, which would cause a funny look from me), I would be forced to ask “30 what?” to get the rest of the information.

        If the author was attempting to capture this caliber-only shorthand in the definition he did it in a confusing way and dropped all the context for how it is used in that manner. He makes it sound like the word “caliber” itself is synonyms with “cartridge” which is absolutely incorrect, and no one I know (even online) ever uses it that way.

    • Jonathan Ferguson

      Not pedantic at all. Cartridge type and calibre are not synonymous and to use them as such causes confusion.

      • That would be nice, sure, but many professional firearms outlets use “caliber” that way all the time. For example, the US Army does.

        • Jonathan Ferguson

          Yep, it’s widespread alright, bit like every AK being an “AK-47”. It’s one of those where I acknowledge the usage,but personally try to use the terms technically correctly.

    • Archie Montgomery

      The meanings of words change over time. (Which is NOT to say anyone can use any word in the manner they see fit.)

      When asked ‘What is the caliber of this rifle?’ – referring to a Mosin-Nagant – one could honestly and correctly answer, “Point three-one-one”. However that does not convey the same degree of understanding as “Seven point six two by fifty-four rimmed”.

      Unless of course the person is asking for the actual bore diameter. And, actual bore diameters are subject to the machinery used, the wear on the cutting tools and perhaps day of the week and time of day. That, of course, is a different discussion.

      Having said that, I’m with you regarding words meaning things. People who use ‘imply’ and ‘infer’ interchangeably should be summarily executed. Anyone who uses the phrase “It’s the same difference” meaning ‘identical’ should be flogged.

    • “With regards to firearms, caliber exclusively refers to the diameter of the bore or projectile, nothing else.”

      Language is one of those things that is extremely organic, and rarely optimized. If I were the nexus of a hive mind in charge of everyone’s thoughts and feelings, I would change the definitions of many words for maximum clarity and minimum confusion… But such a situation is obviously absurd. Therefore, we have to adjust our language not to how we think it should be used, but how it actually is used!

      You say you’ve never seen “caliber” used to mean “the type of firearm compatible with a certain kind of ammunition”, but I highly doubt that. Have you ever heard anyone say “7.62mm NATO rifle” or “9mm handgun”? I would bet you have. That’s precisely how those words are being used, to refer to a firearm not a measurement or the diameter of a barrel, but a firearm compatible with a certain kind of ammunition. Maybe that’s confusing or suboptimal, sure, but it’s been that way since the time of Shakespeare.

  • John


    6. Referring to the personal qualities of an individual

    e.g. – The caliber of a man can be determined by the caliber he carries.

    e.g. – “When I was a boy I carried a .22 short, today I carry nothing but magnums! Not only in my gun, but also in my wallet!”

    • HollowTs


  • Michael Dennis

    In naval circles the diameter comes first say 16″ then the caliber ie a caliber is one times the diameter of the barrel so 16″/ 50 caliber as on a battle ship would be 50 calibers in length.

  • Jonathan Ferguson

    There were no firearms in the 12th century.

    The “kalapous” etymology is also uncertain, if plausible.

    • Rooftop Voter

      The way I feel right now, I was around in the 12th century.

    • I took slight liberties with the age of the word “caliber”, too. The earliest firearms we know of are, what, mid/late-1200s? Something like that. So I think saying “from the 12th Century” a reasonable form, though I think you’re right that it might be misleading.

      And you’re absolutely right about the etymology being uncertain for “caliber”. I don’t know that I’ve ever heard of a word with more than four centuries behind it having a “certain” etymology, so I went with the common narrative.

  • Marcus D.

    What really gets me confused though was when the .36 caliber Colts were
    converted to cartridge revolvers with a Richards-Mason cylinder they
    suddenly became .38s. Now I know that the .36s used a .375″ diameter
    ball, shaved down when loaded to app. .374, and then further reduced
    when going through the forcing cone to about .36 caliber. I also know
    that the modern .38 cal is actually .357, the nomenclature “38”
    apparently resulting because of the case diameter that was designed to
    fit in the .36 cylinder bores. Thus, neither the bullet nor the barrel
    diameter are .38.

  • Don Ward

    Nathaniel confirmed Dr. Evil henchman.

  • iksnilol

    I sorta want to get two cartridges SAAMI approved: 300 AAC and 300 Blackout.

    For bonus points make them incompatible with 300 BLK or each other. Watch the confusion unfold *EVIL LAUGH*.

    • lucusloc

      LoL, something tells me SAAMI would not approve either of those names for new cartridges, for that very reason.

      • iksnilol

        Why? They themselves said that marking a 300 Blackout anything other than “300 BLK” is not allowed.

        • lucusloc

          For the same reason they won’t approve my 5.56 NETO* round. Namespace confusion is their domain, and they are dead set against it for good reason. But I know you knew that already 🙂

          *5.56 NETO (pronounced “neato”, as in “all those gun bits flying everywhere is neato!”) is dimensional identical to 5.56 NATO, but sits a 70 grain projectile on top of 50 gains of bullseys pistol powder (Compressed. And I mean really compressed. With an actual press, probably of the hydraulic variety). The breach end barrel specifications stipulate that it should be able to hold up to a case pressure of approximately a bajillion PSI, and its use in a standard AR 15 produces results that can best be describes using words like “pipe” and “bomb”, usually in that order. If you plan to reload the 5.56 NETO don’t forget to tack weld in the primers, or those suckers are going to pop!

          • iksnilol

            Man, I want to reload some 5.56 NETO.

            Is the hydraulic press we used for pressing in AK barrels good enough?

          • lucusloc

            Probably. Powder compresses really easily*. Pro tip: be really quick with you tack welds. I hear primers are really sensitive to heat.

            *I literally just tested this with some H335, basically the same stuff right?

          • iksnilol

            Can I just use some Locktite? I got the red one.

          • lucusloc

            Sure, if you want the primer to pop and turn the flash hole into a powder fueled cutting torch, thus melting a quarter inch off the tip of your firing pin. Best to play it safe and use a nice strong tack weld, like one of mine. They have been described as “like a hot rivet”*, and we all know rivets are really strong.

            *I believe the exact words were “That’s a weld? It looks like a pile of slag!” but we all know piles of slag and hot rivets are virtually indistinguishable, so I choose to take it as a compliment.

  • John Swinkels

    I get it so when we gauge the caliber of a has nothing to do about his character.You are saying its how big is the fat . Interesting America is full of big calibers.

  • Bobd06

    Most refer to the cartridge when talking about different rounds, caliber us secondary.

  • LT Rusty

    You left out one more meaning: barrel length, usually found in big guns. For example: Mk45, 5″/54 caliber naval gun. In this sense, it means that the barrel is 270″ (54 x 5″) long. Or the Mk7 16″/50, with a barrel length of 800″ (50 x 16″).

    edit: damn, should have read further in the comments- this was already brought up.

  • Lou

    Wait, 7.62 x 54 Remington is not a caliber, it is the description of a case, that accepts a 7.62 caliber bullet. I will give you the fact that the caliber no longer provides data on both the diameter and the weight of the bullet.

  • Archie Montgomery

    Good article, good information for shooters. I’ve found some ‘experienced’ shooters unaware of some of the ramifications of the concept. (I alway have a snicker at expressing ‘caliber’ in metric terms; it is correct to do so, but harkening back to the origin of the term, it always strikes me as ‘odd’.)

    It is also tangentially an excellent exposure to the concept of a single ‘word’, spelled in the same manner, having more than one definition depending on context. Which suggests a working knowledge of English usage and word meanings will assist in much more than passing English class.

    Perhaps (without sarcasm) the author will next address the concept of ‘grain weight’. I have become rather impatient with people asking “What’s the grain?” of a particular type of ammunition.

  • Mike Lashewitz

    Hell I am enjoying the comments as usual and still playing with non Newtonian Solids. I really like the “terminal ballistics” of silly putty. SMILES!

  • Leveller

    Caliber, can also apply to Barrel Length: Length of Barrel divided by the Diameter of the Projectile.