What is Caliber? Bullet Sizes Explained

Understanding bullet calibers, bullet sizes and the difference between them. Bullet caliber refers to the size, or diameter of the bullet.

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You’ve heard it on your favorite cop show, “looks like the killer used a twenty-two,” or, “he was killed with a nine millimeter.” But, if you’re curious like I was, you’re asking yourself, “what the heck is a twenty-two and what does it mean anyway?”

Well, common sense would suggest that the numbers have something to do with size and that is exactly correct. When you hear various numbers being mentioned related to bullets, the number being referred to is what’s called the bullet’s “caliber”. Caliber is a unit of measurement related to a bullet’s size. Specifically, what’s being described is the bullet’s diameter.

Understanding bullet calibers, bullet sizes and the difference between them. Bullet caliber refers to the size, or diameter of the bullet.

click to enlarge (download PDF)

To be even more specific, the caliber of a bullet is the measurement of the diameter of the slug (or projectile) part of the bullet cartridge. This is important because in some situations, the bullet casing will be wider than the slug itself. But the caliber is specifically describing the width of the slug portion. Caliber does not refer to the length or power of the bullet (in most cases), but simply the diameter of the bullet.

The Bottom Line: The Width of a Bullet Determine’s Its Caliber

I know, you’re thinking, “but what’s a twenty-two compared to a nine millimeter?” Well, as with all measurements, there’s the American way and the Metric way of measuring. The metric is simple, a nine millimeter (9mm) is 9mm in diameter. The American measurement is a little different. A twenty-two (or 0.22) is twenty-two one hundredths (22/100’s) of an inch in diameter – or a little less than a quarter of an inch. Similarly, a 0.44 is 44/100’s of an inch, a .50 caliber is a half inch, and so on.


As I’ve been corrected and corrected again, the “inches” measurements are considered part of the “Imperial System” of measurement instituted by Great Britain and retained by some of her former colonies – the most prominent of which is the U.S.A. So, we have metric measurement in millimeters and the Imperial measurement in inches.


As a few have commented below, I want to point out two things in how this page refers to bullet caliber:

First, this page is about bullet caliber, not gun caliber. I make that distinction because a gun designed to fire a 9mm bullet may have a barrel with an internal diameter slightly larger than 9mm (for example 9.002mm). That doesn’t change the fact a gun referred to as a 9mm handgun does fire bullets that are designated as 9mm rounds.

Secondly, I’m not necessarily encouraging anyone to grab a caliper and actually measure the diameter of a bullet to determine it’s caliber. The point of this web page is to explain how bullet calibers have been derived and the names they continue to bare as well as how to most easily compare them to each other. To that end, I feel compelled to point out that It is, in fact, actually extremely common for bullets to be referred to by a cailber number that is NOT the actual diameter of the bullet. For example, the bullet found in a cartidge referred to as a .38 Special is NOT actually 0.38 inches in diameter. You can learn more about that specific round here.

So, just to clarify for everyone: bullet caliber refers to the diameter of the slug portion of the entire bullet cartridge. HOWEVER, the number of the caliber may be slightly smaller or larger than the actual measured diameter of that slug. Each round has its own unique history and perhaps we’ll explore and explain those some day on this site. But, after being criticized for not clarifying those potential and common imperfections in caliber designation I wanted to take the opportunity to explain it here. I hope that this explanation sufficiently covers that.

Thanks, again, to everyone who contributes to this page and site.

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168 thoughts on “What is Caliber? Bullet Sizes Explained

  1. Terry Allen on said:

    I have a Spanish knock off of an s&w 32 revolver what ammo will fit?

    • A Gun Guy on said:

      Being a “knock-off” it’s hard to say with any certainty but the S&W 32 revolver fires a .32 caliber cartridge.

  2. Grant on said:

    I have a question, and it may not be related to this topic at all. In naval guns, for example, the 5 inch gun, why are the diameters of the shells the same but the caliber different? There is the 5″/22 gun, the 5″/55 gun, and so on. Could you clarify that for me please?

    • RyanW on said:

      In artillery, caliber has a slightly different meaning, or rather, the same meaning used in a very different way.

      A typical naval gun might be listed as a 5-inch 55-caliber gun (sometimes written 5″/55). It’s caliber (internal diameter) is 5″, and the barrel is 55 “calibers” long, or 275 inches. It’s merely a way to distinguish between different 5″ guns.

  3. Donna Accettola on said:

    Very,very interesting site. I learned a lot today. Thank you gun guy and all those that contributed. I’m interested in learning about handguns before taking a concealed carry class.

  4. Mary on said:

    Thank you for explaining this. I was reading about the shooting of Pope John Paul II on this 34th anniversary and an article author kept emphasizing the bullet was a 9 mm and I had no idea if that was supposed to be no big deal or extra dangerous to human flesh. Your article did a great job of explaining what caliber is. I especially liked the graphics comparing four sizes. That was very helpful. This is not easily findable information for a layman, so please accept my thanks for explaining what caliber is.

  5. Allen hile on said:

    I have a 1960s British 38 pistol.what bullets will fit it

    • Shannon on said:

      Very helpful and informative with questions I didn’t know I had. Thank you for not choking me on unnecessary BS. Thanks again!

  6. Stephan on said:

    Then why is a .270 Win not called a .277 Win??????????

  7. I was honored to serve in South Vietnam: 68-70, as a helicopter ‘door gunner’, using an M-60 [7.62] but because the Gov’t [Army] would buy the CHEAPEST gun power, our weapons jammed all the time, even though we stripped and cleaned them every night when we got home from our various missions, in a ‘hog trough’ filled with solvent, ready for the next day, 7 days a week, month after month, including all week ends, but I was age 19, full of piss and vinegar… lol., and now age 66. The VC’s [enemy] AK-47 assault rifles were far superior to our goofy AR-15’s and they would work even full of dirt and mud ! Ours would jam all the time! Hey, The VA and the Gov’t still try their best to screw the Veterans, even now days, and look for ways to cut our benefits…. duh. Sorry to get somewhat sour… lol. Our M-60’s and M-14’s took the same ammo as a .306 Winchester, and was a good killing round… but the AR-15 was only made to wound the enemy. Shame. To many Army guys, the AR-15 is but a glorified .22 LR, and very good for varmints and rabbits. email: tschuckman@nullaol.com —Tommy Schuckman. My humble Blog: TOM’S JOURNAL. Beware: the American Dollar will soon collapse. Invest is Silver !

    • I meant that our Army M-60’s and M-14’s used a 308 cartridge … sorry, guys.

      • A Gun Guy on said:

        I want to thank you, Thomas, for taking your time to comment on this article. I want to personally thank you for your service to our country and the sacrifice that comes with that service. We appreciate you adding to our site. God bless!

      • Lou on said:

        As a vet (but stationed in AK)66-68 I want to thank you for your service.

      • Mary on said:

        Thomas and Lou: Thank you for your service!

  8. eric nelson on said:

    Looking at a catalog, cartridges; under caliber it lists 30 30. Than grain..150 well that’s not the 30 of powder i’ve seen mentioned previously , so whats the second 30 again? The more i read the more confusing it becomes. Bout time you think somthing makes sence along comes another explanation which,
    well you get it

    • Brian on said:

      The second 30 is powder. The 150 grain you refer to is the weight of the projectile(bullet).

    • Luke on said:

      I had a similar question about that. Like 30-06, 30-30 etc…my dad was army ranger back in the day, and he says the second number is paying homage to the respective year it was created. 1906 and 1930. Don’t know if that’s true, I would like to say I believe my dad LOL but all this stuff is so confusing! Isn’t there 1 website with all the info and history of each POPULAR round and then we can see where the name actually came from!

      • Stephan on said:

        Luke, your dad’s answer is *almost* correct. I will start by saying this: I have no idea if there is a standard to what the -xx numbers need to be, and there doesn’t seem to be anything set, and the information I’m sharing is true to the best of my memory.

        The -06 in the .30-06 caliber came about because it was created in 1906, same as the very short lived .30-03 caliber. However, with the 30-30 caliber, it refers to the standard 30 grains of powder from when the cartridge first came around. This isn’t really consistent though, as the 25-06 was really invented to be a good bullet that had lower recoil than the 30-06 (it was invented after the -06, and usually has 87 grains of powder). For a real curve ball, there’s also the .250 savage that used to be called the .250-3000 Savage because the bullet would reach 3000ft/s, or the 22-250 which is just a necked down .250 Savage.

        Basically, when a bullet is created, it seems the manufacturer can just add numbers to it for the helluvit.

        • Stephan on said:

          Also, to add to your confusion: 7mm-08 was invented in 1980, typically has 100-180 grains of powder, and usually gets 2,650 – 2,800 ft/s. I think it’s because it’s parent cartridge is the .308, so my guess is that the -08 gives tribute to that, though the .243 is also a necked-down .308 round.

          Sorry if you now know less than you started.

    • A Gun Guy on said:

      Well, Don, it’s a little difficult to tell from these photos. At first glance I would say it’s a .308 rifle cartridge. The bullet probably weighs beteween 160 and 170 grains. But without specific details on what we’re looking at it’s hard to be sure.

  9. Kevin on said:

    I’m trying to find out where rifle sized ammo ends, cannon rounds begin, and artillery rounds begin. For example it always been my understanding that 20mm is considered where cannon shells are considered to begin, but does it end at 37mm? 40mm? What size is artillery considered to begin?

  10. ksha on said:

    can i use any other ammo in .35 remington the game master 141 model pump action

    • mike walbridgee on said:

      Clearly written and understandable try telling some logerhead a 38 a 357 and a 9mm are the same bullet

  11. mike on said:

    So, what diameter slug (projectile)will successfully reload into a single shot 410 shotgun with a full choke?

    • A Gun Guy on said:

      Depending on manufacturer, a .410 shotgun slug is .372 inches in diameter. If your question is in a search of an alternate round to fire from a .410 shotgun, there is no good or right answer. You should never load a cartridge into a gun it wasn’t designed to fire.

  12. Ken on said:

    Excellent article.
    I have often wondered about this.

  13. Janet on said:

    Hello, I am doing a speech for my speech 101 class about weapons to use for a zombie apocalypse and i was trying to find information on how far can a bullet travel and how fast. Also, I wanted to know how far can a gunshot sound travel?

    • salty on said:

      the sound of a firearm discharge will vary depending or the weapon and topography. although most un-suppressed discharges will be heard from a long way. difference being; a .22 can be identified from about a km away over flat ground, whereas a .45 will be noticed at maybe 2 or 3km. (echos may amplify this). automatic fire will be easier to identify.

    • Sandra on said:

      Awesome…A+ speech for sure!

    • Jim on said:

      Is this what schools should be teaching?

      “How to efficiently kill a large amount of zombies/people”

      Sandy Hook wasn’t enough?!

      • A Gun Guy on said:

        Jim, no one suggested teaching any of this information in schools. Where do you get that assumption? As for killing zombies, that’s a purely rhetorical discussion, not meant to be taken literally. “Sandy Hook wasn’t enough?” Enough for what? What point are you trying to make? Guns kill people? Guns are evil? If you have something to say, say it.

  14. Bugs on said:

    Like some of your contributors I am a non-shooter but have had the same questions. My simple math calculation indicates that a 9mm projectile measures .354 inches, very close to the .357. Are they ever interchangeable or does this rely on cartridge size/barrel bore?


    • A Gun Guy on said:

      Bugs, while the diameter of a 9mm and a .357 round are very similar, there are a few key differences. For one, the .357 magnum cartridge has a lip at the base of the casing that helps to hold it in a revolver. This would not fit in a typical semi-auto 9mm handgun. Secondly, the .357 magnum charge is larger than that of a 9mm and would be potentially dangerous to fire from a 9mm pistol if you could even fit it in. Also, the .357 cartridge is nearly a half inch longer than a 9mm.

      So, to answer your question, no .357 and 9mm cartridges can not be interchanged. It is always best to only fire ammunition that your firearm was designed to shoot. Interchanging rounds with the wrong gun can be very dangerous.

    • quintin on said:

      A .38 special can be fired in a .357 magnum but never vice versa . To do so would be very dangerous as the .357 is more powerful. A .380 auto can be fired in a 9mm handgun the only difference is the .380 has about 1mm shorter casing and lighter load it probably will not have enough energy to cycle the next round. Shooting a 9mm cartridge in a .380 auto pistol would be very dangerous and should never be attempted for the same reason. The revolver style rifle Rossi Circuit Court judge fires both .410 shotgun shells and .45 colt ammo interchangably.but if you put a .45 Colt in your old shotgun make sure your life insurance is paid up A .30-30 Win.and a .30-06 Spgfld and a .308 Win. all have a nominal bullet diameter of .309 but none of these three cartridges are interchangeable. The .308 however is also same round as the 7.62 x 51 nato round. Some cartridges have rims others are rimless. High power rifle cartidges have a bottleneck design that is unique. The original designer of each of these calibers is often attached to its name such as .45 long colt or .30-06 Springfield. Getting back to the question. If you have to ask an online stranger whether something of this nature is safe you really have no business messing around because you have no credible knowledge on which you are basing a decision that has the potential to take your life.

      • highmiles68 on said:

        I can’t speak to the first part of your comment, personally I only ever use ammunition that is stamped on the barrel but I agree 100% with you about asking strangers, or anyone for that matter, if a firearm can use ANY ammunition other than the round that is designated for it. Anyone who has to ask should really consider taking a firearms safety course. So please people before trying to shoot ammo in a firearm it’s not designed for do a little research on what can happen when things go wrong.

    • Dirty Dave on said:

      Bugs, as others have said a 9mm and 357 are never interchangeable and although the information was in some of the other answers a non shooter may not have picked it up. The biggest difference in the bullets is that they were made for two different types of guns and so their construction is different. As someone else pointed out the.357 has a lip because it is made for a revolver. The lip allows the bullet to be seated into cylinder as well as helps as assists in ejecting the spent casing. The 9mm also has a lip, but unlike the .357 the lip is no bigger than the casing. Also and most important the 9mm is made for a semi-automatic weapon so it’s not just the bullet difference but the gun difference that makes the swap impossible. To my knowledge there are only 2 occasions when bullets can be used in different guns. As said, a 38 can be used in a 357 but a 357 can not be used in a 38, both weapons are revolvers but a 38 is not designed to handle the energy of 357 bullet and would be very dangerous to try. And in rifles a .223 can be used in a weapon built to shoot 5.56 bullets but a 5.56 bullet can not and should not ever be used in a rifle designed for .223 bullets although it probably wouldn’t fit it would be dangerous to try. I have read somewhere in the article that a .380 can be used in a 9mm, but not the other way around. I have to admit I have never heard of this being done and would not advise it, the 380 is much smaller and lighter and the the 9mm pistol is just not made to handle this size round. I hope this makes things clearer.

      • Raul on said:

        A .357 and a .38 special, can both be fired from my Henry Big Boy. That rifle has no issues firing either one of those rounds.

  15. Josh on said:

    In trying to figure out the best all around hunting rifle for deer and elk since there is a big size difference between the two animals.

    I know the 30-06 is popular but I’ve heard people swear by the 7mm and the .308

    I’m thinking this is just a matter of preference but any input would be appreciated since I’m new to the hunting scene.

    • Ronald on said:

      Ok my opinion would be in your case as in many a hunters . To have a versatile round . Surely I say the 30.06 adequate for both medium and large big game . Deer and Elk. Now the 7 mm “7mm Remington is a step up from the ’06 and recoil is more noticeable. I say 7mm a bit overkill for deer per say.
      Now on the other hand the .308 is a step down from ’06 . Although a very accurate round not as much recoil and although great for medium size big game the deer . It nots the best choice for Elk as far as knock down power . But your choice. So it boils down as always for the caliber to do it all in North America it’s definitely the 30.06

  16. Christof Rauch on said:

    Hi, I have a .22 bolt action Targetmaster 510 single shot. Can I fire a .17 HM2 in this rifle (i.e. could I use it as an emergency “backup” round)?

  17. Bruce on said:

    Why is there no talk about a .32 revolver? I have one that I carry. What is your view on this gun?

  18. Jason on said:

    So I’m confused, what’s a .30-06? Or a like Winchester/Marline repeater takes a .30-30, what the difference? What’s the second number for? What does it define?

    • A Gun Guy on said:

      Hi Jason. This has been asked a couple of times. The .30-30 Winchester was one of the earliest small bore sporting rounds in the USA back in the late 1800′s. The second “30″ represents the 30 grains of powder in the round. The .30-30 was the predecessor of the .30-06.

      The .30-06 Springfield (it’s pronounced “aught” as in another word for “zero”) was introduced in 1906 (hence the 06). The round was adopted as US Army standard issue and remained such until the 1950′s when it was replaced by the 7.62x51mm NATO round (also called the .308 Winchester). Most .30-06 cartridges pack 50+ grains of powder giving it a larger charge than .30-30 Winchester.

      Hope that helps.

  19. Charles Neuhaus on said:

    I recently purchased a 1910 9mm German military Luger. On the barrel is stamped 8.82. Does this refer to the actual caliber?

    • A Gun Guy on said:

      Charles, unfortunately, I can’t find anything in my research to explain the 8.82 on your pistol. The luger was introduced in 1908 as the “Pistole Parabellum 1908” for the 7.65×21mm Parabellum round. It was later replaced with the 9mm parabellum by Walther. Nothing in the information I have shows any measurements close to the 8.82 noted on your gun. It could be a manufacturing location or something else. I’m sorry I can’t tell you any more. In any case, that’s an old and pretty rare firearm. You’re lucky to have it.

      • Charles Neuhaus on said:

        Dear “A gun guy”, Many thanks for your help. The 8.82 is on the bottom of the barrel, next to the frame and between the serial number and the frame. The Luger is in very good shape and has a unit marking on the grip, 2nd Guards Dragoon. After I get it checked out by a gunsmith I intend to fire it.

        • A Gun Guy on said:

          Charles, I just Googled “8.82 caliber” and landed at a Wikipedia page. This might explaine the number but I don’t trust everything on Wikipedia:

          “The cartridge headspaces on the mouth of the case.[18] The common rifling twist rate for this cartridge is 250 mm (1 in 9.84 in), 6 grooves, ø lands = 8.82 mm, ø grooves = 9.02 mm, land width = 2.49 mm and the primer type is small pistol.”

          Not sure if that’s it or not. Anyway, would love to see a photo of the gun. If you want to send one to us you can email admin@nullgunsandammo.info. Have fun with it!

  20. Syed Mohammad Abbas on said:

    Excellent information

  21. Lucas on said:

    I’ve definitely found myself asking those very questions when watching TV or a film. I always wondered what calibre related to. I think a lot of people instantly think of power when it is simply the diameter. Thanks for the illustrations; they really help. Do they come in set sizes? Or custom? The important thing is to be safe with them.

  22. NikkiB on said:

    I like my Walther P .38 but both my glocks (19 & 26) are easier for me to conceal and I would prefer them over my Walther P .38 any time in the need of protection. But both use 9mm so its even better that I don’t have to buy different kinds of ammo except for the biretta and the Remington 870 full choke shotgun :)

  23. Cameron Hamill on said:

    Thank you so much for your post. It’s fantastic.

    I wonder if you could please add two more rifles?

    .270 Winchester
    .303 British

    I don’t know very much about Firearms but I believe these two Rifles are quite popular.

    Thanks so much.

    • Niel on said:

      The bullet diameter of the .303 British is approximately .311″.

  24. What firearms that propel projectiles with diameter of more than 1 inch?

    • sushan tripathee on said:

      Anti-air or anti-tank weapons… nth that you can just carry around

  25. Mike Kinard on said:

    Well .380 Is smaller and less powerful than a 9mm and is typically designed for a semi-auto gun/pistol. Now the.38 sig and the .38 special is alittle bit morep powerful than a 9mm and alot longer in size, and it’s made to be shot from a revolver. Hope this helps you.

    • NRNS on said:

      .38 Special is NOT more powerful than 9mm. Get your facts straight.

      • Thomas Kelley on said:

        Easy NRNS! Everyone knows that the 9 mm is superior in velocity, f/ps and energy (in ft/lbs.) but many people swear that .38 special has more stopping power.

        • Ryan Marchant on said:

          You’re right Thomas, the .38 does have better stopping power, and it’s because the round is slower then the 9mm, even though they’re about the same size the slower speed is what gives the .38 more stopping power

          • smithandwesson93 on said:

            “Knockdown power” is largely a myth. The real “stopping” is not caused by the impact of the bullet, but how it affects the internal organs. Blood loss (i.e.; hitting a major artery) is what really disables the perp.

      • Kirk on said:

        If you look at a 38 special and 9mm side by side you will see that the 38 special is considerably larger with a slightly larger slug. The jacket holds more powder. It is a more powerful round than a 9mm and has more stopping power. As far as the effect on internal organs, a hollow point will do much more damage than a solid bullet.

      • Ronald on said:

        That’s right I agree bad info stating that .38 is more powerful then the 9mm . The 9mm is a hotter round more velocity that’s why it’s got bit more punch I pretty sure about this . It may be shorter but I believe as an educated guess that the 9mm is a larger projectile in grains . Now does out there please help me I wouldn’t mind being corrected if need be

  26. great website, lotta of knowledge. what is the difference between the old .38 and the 380. It looks the same as far as the math goes? Also, is the 9mm the same as the .38?

    • A Gun Guy on said:

      Russ, Mike’s comments are correct but there is a bit more to the .38 caliber. The “old .38” that you are referring to is most likely the .38 Special designed by Smith & Wesson in 1898. You can read more about that particular round here http://bit.ly/UtMdN9. One thing that is important to note is that the .38 Special is NOT 0.38 inches in diameter. It’s actually 0.357 accross. It was designed as an alternative to the .38 Short Colt which itself, was a replacement for the cap and ball firing Colt 1851 Navy Revolver. So, even though the diameter is smaller, the .38 remained in the name of this cartridge.

      In addition, it’s important to note that there are other 0.38 rounds:
      .38 Long Colt (true diameter 0.361″)
      .38 Short Colt (actually 0.359″)
      .38-40 Winchester (diameter is 0.401″)

      And then there’s the .380 ACP (Automatic Colt Pistol) which is commonly referred to as a Short 9. The bullet in this cartridge is the same as the 9×19mm Parabellum cartridge – also referred to as 9mm Luger – which is the most commonly used 9mm ammunition. Both the .380 ACP and 9mm Luger use a bullet that is 9.01mm in diameter or .355 inches.

      So, the long answer to your question is that the .380 ACP round has more common with a 9mm Luger than a .38 fired from a revolver. In all cases though, .380 ACP is the shortest cartridge of the lot.

      Glad you asked?

      • Kelly on said:

        Do not forget the .357 Mag, it is to the 9mm Lugar what the Lugar is to the 38 Special. If you want to shoot out to 50- 70 yds instead of 30-40 get this one.

  27. Arnold Rimmer on said:

    How did the sizes come to be?

    In some cases the size is right on a fraction but most cases they are just off by ±.02.

  28. Nathan on said:

    Hi there, someone wrote in the following and I just have a question regarding this…

    All three are similar in that the all fire .308 caliber rounds, meaning the slugs used in all three are .308 inches in diameter. The differences come in the case sizes and loads (amount of powder).
    The .30-30 Winchester was one of the earliest small bore sporting rounds in the USA back in the late 1800′s. The second “30″ represents the 30 grains of powder in the round. The .30-30 was the predecessor of the .30-06.
    The .30-06 Springfield (it’s not “odd”, but “aught” as in another word for “zero”) was introduced in 1906 (hence the 06). The round was adopted as US Army standard issue and remained such until the 1950′s when it was replaced by the 7.62x51mm NATO round (also called the .308 Winchester). Most .30-06 cartridges pack 50+ grains of powder giving it a larger charge than .30-30 Winchester.
    There are actually several different types of .300 caliber cartridges out there varying in size and load. These are less commonly used than the .30-30, .30-06 and .308 Winchester.

    With a 30-30 if the second 30 represents 30 grains of powder in the round, then doesn’t the 06 in a 30-06 round mean 06 grains of powder obviously it has more than 6 grains of powder , but following the above explanation wouldn’t that be correct?

    • Darius on said:

      The .30-06 was introduced after the .30-30, in 1906. I know this is a bit confusing since the relevance shifts from grains of powder to the year it came out. But Winchester differentiates the two rounds with the YEAR that the .30-06 came out: 19″06″. The .30-06 still packs more powder than the .30-30. Hope this helps!

    • Kelly on said:

      The 30-06 was designated that after it was adopted by the U.S. military. This is the simple way; a caliber measures the bore of the gun, a 30 caliber has a .30″ bore. The bullet is measured from the outside dimension. The true 30 caliber usually have .0375-.04 lands so if you add the land measurements to the bore you arrive at .308. Usually metric designated cartridges are measured by bore also but use the metric. You can figure this out pretty easily by multiplying the bore by 25.4, (.30 X 25.4= 7.62mm). The metric would divide by 25.4, (7.62 / 25.4= .30) The barrel it is used in would then be measured for land depth. Common 30 cal. bullets may have an added .008″ so the imperial would be .308″ bullet diameter or 7.82mm. The metric designations mostly still have the European military tags attached to them. A 7.62 X 51 means a 7.62 bore inserted in a cartridge 51mm tall. Sometimes this is simpler than naming different cartridges with names as Americans sometimes do. The 7.62 X 51 is .308 Winchester in America. The 30-06 Springfield named by the U.S. army because Springfield supposedly developed it is the 7.62 X 63 in Europe. Hope this helps.

  29. Phil on said:

    Why do people like using a .22 instead of a .25? Is it because of the velocity, .22 does like 1300 and a .25 does like 800.. but the .25 will do more damage in the end IMO because it has a bigger grain size

    • Mike Kinard on said:

      Actually my friend, the caliber of the .22 is obviously smaller than the .25 But the .25 is actually less powerful and has less penetration power due to the lighter round, the .22 takes longer to slow down at the same velocity.

  30. luggage on said:

    ok so a 22 is 22/100 of an inch diameter – BUT whats a 22LR / what designation works in guns ? versus rifles ? are there 22’s with centerfire versus rimfire ?


    • A Gun Guy on said:

      When it comes to .22 caliber, there is no distinct designation for handguns versus rifles. There are both rifles and handguns that fire the traditional .22 as well as .22LR and .22MAG. The .22LR is short for .22 Long Rifle. This round is also a rimfire and was designed with a larger charge for longer distances initially to be used in a rifle. Hence, the “long” refers to the longer cartridge to contain more powder for firing in rifles. However, there are also handguns that are designed to fire the .22LR as well, so it is not a “rifle only” round. Same for the .22 Magnum which has yet a larger cartridge and stronger charge than the .22LR.

      There is a .22 centerfire cartridge: the .22 Hornet. As far as I know, there are no handguns designed for this round as it is a high-powered rifle round with muzzle velocities as high as 3,000 fps. That kind of velocity makes this type of cartridge very close to the 5.56mm or .223 rifle rounds that are used in common hunting, sporting and even military rifles. It is nowhere near as commonly used as either of those rounds, but there are a number of manufacturers that offer rifles for that round.

      Overall, the .22LR is the most common firearm round used in the world. It is cheap, very accurate and is used in a variety of firearms. Maybe people just getting into firearms start with a pistol and/or rifle that fires the .22LR. It’s a good round to learn with given their low cost and (typically) high availability. Most of the other .22 rounds are a more of a novelty than a commonly used cartridge.

    • Mike Kinard on said:

      The .22 lr is just longer in size and usually comes in magnum rounds, they are a more powerful version

      • highmiles68 on said:

        I’ve never heard of 22 lr magnum, there’s 22 short, 22 long, 22 long rifle & 22 magnum. All of these are a rimfire cartridge with velocities from about 700 fps to 2200 fps. The 22 lr is the most common and is available in a low velocity/quiet version, standard velocity & high velocity with various bullets such as round nose, hollow point, fragmenting, etc. depending on the intended usage, there’s even a shot shell version available. 22 short & 22 long are less common today but not obsolete although 22 long can be very difficult to find.

  31. John Webb on said:

    A cast 9mm bullet should be what size? 3.56 or 3.55? I am using Alox lube and a Lee 2 X 3.56 mould and the bullets vary from 3.56.5 to almost 3.57, so I was told by Brownells to size all my case bullets at 3.55 and a second coating of Alox and then load! What say you? And what are your qualifications in giving advice?

  32. don roupp on said:

    Do they make a .25 cal. revolver? I can’t remember ever seeing one.

  33. DJW on said:

    can you help explain on rimfire and centerfire more? I know the basics, just want more specific understanding

  34. Does a .44 .40 mean the bullet ( projectile ) is 44 hundreths of an inch…and the .40 is the powder casing of the shell? Does this make it a 40 caliber? Is this just 1/001 of an inch smaller than a .45 caliber?

    • Howard on said:

      I meant to say does this make it a .44 caliber? If so, then why not simply call it a .44

      • A Gun Guy on said:

        Fair question. The .44-40 was created by Winchester arms way back in 1873. It is a .44 caliber (although technically, the bullet is 0.427 inches in diameter – the neck is .443). The second number, the “40” used to refer to the 40 grains of black powder that was used to charge the round. Over the years, the bullet slug weight and charge have varied and are now available in multiple combinations. However, since the cartridge is quite unique, no matter what the charge or bullet weight, it’s still referred to as a .44-40. Firearms terms have a funny way of not changing over time.

  35. Elizabeth on said:

    This is great info and helps a lot! Thank you! I’m getting my first handgun this week and wools love any suggestions! I’m a female looking for personally protection in a gun compact enough for a purse but not tiny. I think I’ve determined I want more than a .22 (probably a 9mm or .38) and a SA pistol but that’s as far as I’ve gotten. Any suggestions?

    If it helps I’m 5’6″ and I consider myself pretty strong.

    • Elizabeth on said:

      Wow typos… Sorry I’m on my phone!
      Would** love any
      Personal** protection

      • A Gun Guy on said:

        Hi Elizabeth. Glad the site is helpful to you. If you’re looking for a personal protection firearm, as much as I love the Ruger SR22, I agree that a .22 doesn’t have enough stopping power. If you’re going to carry your firearm, be sure to check your state laws about concealed carry. I know certain states prohibit you from carrying your gun with you.

        Beyond that, I would agree that a 9mm or .380 would be your best choice. There are some enthusiasts that insist nothing less than a .45 is adequate for personal protection, but I don’t agree with that opinion. Just about all police officers in the United States carry 9mm, so if it’s good enough for them, I think it’s good enough for the rest of us. The .380 round is the same diameter as the 9mm, but the casing is a little smaller resulting in less muzzle velocity. The .380, also referred to as a “9 short”, is the most common carry caliber chosen by women. I think that is because it combines a similar stopping power of a 9mm with a more desirable recoil. Guns and Ammo magazine recently did an article about compact personal defense pistols that might be helpful (http://bit.ly/LLQgq1). I’ve heard a lot of good things about the Beretta Nano and I know Ruger has a great reputation for their LC9 and LC380 pistols. Personally, I like the Beretta PX4, but that’s not as small as the Nano and LC’s. I would definitely recommend talking to your local gun shop for their recommendations as well. Hope that helps.

  36. Kelford Woodard on said:

    what does 7.62×54 mean?

    • A Gun Guy on said:

      7.62×54 is referring to the bullet size. It is 7.62mm wide by 54mm long.

      • Brad on said:

        Slight correction in order here: 7.62 refers to caliber (bullet width) in millimeters, 54 refers to case length in millimeters, measured from case neck to case head.

  37. rd on said:

    What guns use cci 17 ammo

    • rd on said:

      OK so cc I is a brand… My question is what weapon s are 17caliber

      • A Gun Guy on said:

        Yes, CCI is a brand. The most common .17 is the Hornaday Magnum Rimfire (.17 HMR). There are a number of rifles and a few revolvers that fire that round. Savage Arms and Marlin make some nice target rifles for that caliber and I believe Ruger makes a revolver in that round. Like .22 caliber, .17 are mostly for varmint or target shooting. Impact Guns carries quite a few models if you check out their website you can see: http://www.impactguns.com/firearms.aspx?Caliber=17+HMR+Hornady+Magnum+Rimfire

        Hope that helps rd.

        • rd on said:

          It does help…. My education continues. It’s nice to have a site where I can ask about what seems to be common knowledge to experienced gun guys. I found the descriptions on your recommended site very useful. Thanks

          • A Gun Guy on said:

            Happy to help rd.

  38. Just to point this out, the British use the Metric System, not the U.S.
    So you have it backwards.
    The U.S. Measures in inches (.308, etc)
    The English use meters (mm instead of inches, km instead of miles, etc)
    Just saying, you may want to make corrections. :)

    • A Gun Guy on said:

      Fair point. I was thinking more of the English language rather than “English” as British. You are right, the metric system is used by the British. It’s us Americans that have our own way of measuring to make things complicated. Thanks for pointing that out.

      • dave on said:

        british use metric and imperial. eg use miles/inches/pounds/stone but metres/cm for some things…mostly imperial though

        • dave on said:

          lol nm, just seen comment below

    • Richard Miller on said:

      As an English man I would like to politely correct you on the terms used. There is the Metric system or SI (French) system International which is the European standard, In Britain (England, Northern Ireland, Scotland and Wales) we still use the Imperial system, mixed with the metric system that is :- Feet, Inches, Pints Gallons, Miles and so on, where it becomes confusing is the metrification of the inch. I will try and explain, we turn the inch into a percentage, part of 100 so a quarter of an inch is not 1 over 4 but 25% or 0.25. Half an inch is 1 over 2 but we all call it “50 cal” point five of an inch. So to clarify I am English my passport says I’m British, we gave all our Ex colonies (sorry) the Imperial system. This is a similar problem on European tyres where the sizes are a mix of metric and imperial and the imperial is written in in the percentage format like 6.75 inches, The Imperial system will never go because of USA influence around the world I give a good example of your Aircraft industry, how many 747s are held together with torque settings in pound/feet, good thing to.
      Look forward to your reply

      • A Gun Guy on said:

        Your correction has been noted. Thank you for your kindly input.

  39. ThePelikan93 on said:

    Oh, and could you talk about what a “magazine” is?

    • A Gun Guy on said:

      We’re actually planning a post on this topic to help the common misunderstanding about “clips” and “magazines”. The short answer is that a firearm magazine is a container that holds multiple rounds of ammunition. A magazine can be internal (common in shotguns and many rifles) or detachable which is most common in semi-automatic handguns and sporting rifles.

      Magazines are different than ammo “clips”. A clip is usually made of metal and is used to hold several round of ammo together so they can easily be inserted into either an internal or detachable magazine.

      To understand the basic difference, someone once compared paperclips and everyday printed magazines to ammo clips and mags. Put simply, you can always insert a paperclip into a magazine, but not the other way around. The same is true of ammo magazines and ammo clips. Hope that helps. We’ll definitely post more on that in the future. You can sign up for automatic email updates here: http://www.gunsandammo.info/subscribe-updates

    • spritom on said:

      A magazine is a working machine by itself. It has moving parts such as the internal spring that moves the ammunition along the magazine from the bottom to the top. The purpose of the magazine is to have a round of ammunition ready at the top of the magazine for the gun to grab the cartridge when it needs it.

      This is similar to a magazine in a battleship that might be 3-5 stories tall and moves the ship’s ammunition from the bottom of the ship up to the deck for the guns (using elevators and other moving parts).

      A PEZ dispenser is a type of magazine.


      A clip has no moving parts and simply bands the ammunition in place. Similar to the function of a paperclip that simply holds paper in place or a hair clip that simply holds hair in place.

      There were guns in the 20th century that used clips, but today it is more common to see a “stripper” clip that is used to load a magazine.

    • Mike Kinard on said:

      A magazine also known as the clip is just what holds the ammo for semi auto handgun, types of rifles, machine guns.

    • terry on said:

      A magazine is a glossy publication with pretty pictures. Sorry I’m a news person couldn’t resist. Nice site looking at replacing a gun I just broke and was mulling over calibers. Nice to see all the info and comments.

  40. ThePelikan93 on said:

    Hi!! :) Thanks a ton for this website!! :) Am taking a Forensic Pathology course, and studying terminal (wound) ballistics. The whole jargon was lost on someone like me who knew nothing about guns. Been reading books and stuff, but wasnt really helping me as everytime they said something remotely technical, i lost it!! Your website really helped nail the basics, so i can actually understand what my books are getting at.

    • A Gun Guy on said:

      ThePelikan93, it makes us very happy to know that the information here can be helpful to you. Please feel free to ask any questions if we can be of any more assistance.

  41. Britt on said:

    I just bought a Rossi 22/410 combo and was wondering which bullets would be best for each caliber? We plan to shoot animals ranging from squirrels to a deer.. Would love to hear feedback on how well you liked the gun (if you’ve shot or owned one ) and which bullets would be best. There’s just so many to choose from is why I’m asking on here. Any info on this will be greatly appreciated!

    • A Gun Guy on said:

      That’s a great and popular combo gun that’s affordable and offers variety. You definitely don’t want to use the .22 when hunting deer. Those little rounds are for small game that will provide some challenging targets. I’m admittedly not a hunting expert, but I like the CCI .22LR rounds a lot and they are well respected. They have a 36 grain hollow-point and a 40 grain round nose that, I suspect, would be fine for hunting squirrels and other small game. As for the .410 for taking down deer, I’m going to have to defer to some others here. As I said, I’m not the most experienced hunter. While .410 is capable of taking down a deer, I’m pretty sure you’re going to want to be pretty close to take ’em down with one shot. I’d probably go with Federal or Remington slugs or 00 buck. But, as a I said, I would like to see what others recommend.

  42. Lorie F on said:

    I have a 17 Caliber rifle I went to buy some shells they handed me shells that said 17 caliber but they looked like a 30/30 shell they wont fit my gun so whet kind of gun is that shell used in curious!

    • A Gun Guy on said:

      Lorie, is your rifle designed to shoot .17 caliber HMR rounds? If so, that’s all it will take. The .17 HMR is a rimfire round – which means it doesn’t have a centerfire charge. You can tell that easily by looking at the bottom of the round. If there is a small disc or circle n the middle of the base of the round, then that is a centerfire cartridge and not meant to be fired in your rifle. If is doesn’t have that, and it fits your rifle, than it would appear to be a .17 HMR.

      • Lorie F on said:

        Thank you for your input very helpful

  43. N. Belal on said:

    In Bangladesh one can own non prohibited bore (N.P.B) hand gun. N.P.B is defined as any caliiber up to 0.32 oe 7.65MM. The law was framed in 1873. Would 0.327 caliiber be considered as non prohibited considering that the diameter of both is same.

    • A Gun Guy on said:

      N. Belal, I can’t speak to the legality of a firearm in another country. Unfortunately, I’m not familiar with the N.P.B. laws of Bangladesh so I can’t tell you if a 0.327 caliber would be legal or not. I would consult a local lawyer on the subject. Sorry, I can’t be of more help.

  44. DB on said:

    What is the difference between a 30 30, 30 odd 6, and a .300 bullet?

    • A Gun Guy on said:

      All three are similar in that the all fire .308 caliber rounds, meaning the slugs used in all three are .308 inches in diameter. The differences come in the case sizes and loads (amount of powder).

      The .30-30 Winchester was one of the earliest small bore sporting rounds in the USA back in the late 1800’s. The second “30” represents the 30 grains of powder in the round. The .30-30 was the predecessor of the .30-06.

      The .30-06 Springfield (it’s not “odd”, but “aught” as in another word for “zero”) was introduced in 1906 (hence the 06). The round was adopted as US Army standard issue and remained such until the 1950’s when it was replaced by the 7.62x51mm NATO round (also called the .308 Winchester). Most .30-06 cartridges pack 50+ grains of powder giving it a larger charge than .30-30 Winchester.

      There are actually several different types of .300 caliber cartridges out there varying in size and load. These are less commonly used than the .30-30, .30-06 and .308 Winchester.

      • DB on said:

        You are the greatest! Appreciate your detailed feedback. Thanks Gun Guy!

        • A Gun Guy on said:

          Happy to help DB.

  45. William R Durham on said:

    Whats the differance between a 22 and a 10/22. Is the 10/22 to much gun for squirrel hunting?

    • A Gun Guy on said:

      There are a number of different .22 caliber rounds out there. There’s the typical .22 also known as the .22 short, there’s .22LR (or .22 long rifle) and the .22 magnum. All are .22 caliber but carry different loads meaning the amount of powder is different. The .22LR is not only the most commonly used of the .22 varieties, it is also the most common caliber used in the world. The 10/22 is not ammunition but a rifle produced by Ruger that fires .22LR rounds.

  46. cliff on said:

    I’m really confused on caliber. I’m wondering how a 5.56mm Nato round can show it is .224″ dia., When 5.56mm is .219 inch diameter. I know that’s not a whole lot difference, but I thought even a little difference could be a problem in rifle I.D. What am I missing here, or has some regulating body just given the 5.56mm caliber the same ID as the .223, even though the actual diameter of the bullet is smaller?

    • A Gun Guy on said:

      I know some diehards will probably wanna punch me for this, but the English measurements in inches are not always dead-on. The Metric versions, however are typically exact. I know the round was created by Remington, but I don’t know why they introduced it as .223 rather than the actual .224 diameter. But, it’s not the first time an English measurement wasn’t accurate. One other example: the .38 special is not .38″ but is actually .357″ in diameter. There’s a whole history of why that is. You can read about that in this article: http://www.gunsandammo.info/blog/educational/something-new-i-learned-about-the-old-38-special

  47. Bobby on said:

    This was very helpful. Thank you very much for the info. I am trying to get a better knowledge of firearms, and this site is very useful.

  48. If I wanted something bigger than a .22 but smaller than a 303 what would be a good choice

    • A Gun Guy on said:

      Are you talking about rifle rounds or handgun rounds? For handguns, the only common option would be the .25 ACP or a .22 magnum. For rifles, there are more options. The most common are the .22 magnum, .223/5.56 NATO, 22-250 Remington, .243 Winchester or the .270 Winchester.

  49. Angela on said:

    Does anyone know what the entry demension would be using a .25? Please forward answer to angelar777@nullgmail.com

  50. John Teeny on said:

    Hello Gun Guy. Thanks for the blog. Couple of questions:
    1. How does person tell what caliber a gun is?
    2. Can a rifle be machined to a different caliber?
    3. How does grain play a factor?

    • johny on said:

      #1 its on the barrel #2 yes its a lot of work but yes you can go bigger but not smaller#3 bigger caliber bullits are typically heaver grain.. some twist rates require or shoot more accurately with different grain bullets. It all depends on what each gun likes thats why alot of people like myself reload their own ammunition.

      • smithandwesson93 on said:

        Sorry to correct you “Johny,” resurrecting a really old thread, but you’re dangerously wrong on #2, and I don’t want anyone to get hurt.

        You can safely go smaller, but not bigger. For instance, many popular handguns (most notably Glocks) chambered in .40 S&W have conversion kits to enable them to fire 9mm, but not the other way around. Similarly, revolvers chambered for .357 magnum can fire .38 spl, but even if you were able to fit a .357 mag into the chamber a .38 weapon, it would most likely blow up the weapon (and your hand).

        This is because the pressure tolerances are tailored to the original caliber of the gun. Simply put, they can safely handle less powerful rounds, but rounds that are higher powered than the original design compromise the structural integrity of the weapon.

  51. Bud on said:

    I have several boxes of 303 British Remington ammo, I did a bullet test on the muzzle of my 303 and the bullet went all the way to the casing, indicating the bore is shot out, using a bullet from one box, but I also used a round from a different box and it was a good 1/4 inch from the casing, so now I’m totally confused. I don’t have a micrometer, to measure the bullets. Anyone got any ideas why so much difference between the rounds? I called Remington and talked to a quality control person, they told me to send the box of ammo that was too small to them, they replied by letter and told me everything
    was in tolerance, but why is there so much difference between the two different boxes,
    and made by the same company?

  52. bucky on said:

    Im tring to find out what size bullit will work in my 12mm black powder pistol from spain

  53. Frank on said:

    Hi Gun Guy. Is there a difference between a .40 caliber and .40 s&w caliber? I see s&w all the time and don’t know if there’s a difference.

    • Mike Kinard on said:

      No the S/W just stands for Smith and Wesson

  54. kenneth on said:

    Hi gun guy, I got a .38 special taurus snub nose. Love the gun, but was wondering whether there is an semi auto version that is compact and has the same caliber?

    • A Gun Guy on said:

      As far as I know, there are no semi-auto pistols designed for .38 special ammo. I could be wrong, but I believe only revolvers are designed to shoot that round. It could be because of the length of the cartridge or just because the .38 special was designed for revolvers to begin with. But, I think the snub nose revolver you have is the most compact version you’re going to see for that round.

      • johny on said:

        38 special is a rimmed cartridge they do not make an auto for rimmed cartridges like the 38 special

      • Doug on said:

        Henry Repeating Arms company makes a rifle for .357 mag
        and .38 special. Henry model#H006M

  55. Derrick on said:

    Hey there , what is a 22-250 is it a 22 or 250?

    • A Gun Guy on said:

      The 22-250 is a rifle round. The bullet itself is .224 in diameter but the diameter of the casing is .254. Like a 5.56mm or 7.62mm NATO round, the casing is bigger than the bullet which is why it has two numbers in it’s name.

  56. mike fogg on said:

    Why does a 45 appear as larger than a 9mm–am I thick?

    • A Gun Guy on said:

      No you’re not thick. .45 is larger than 9mm. 9mm is closer to .38 caliber so .45 is definitely larger.

  57. Jeremy on said:

    You should also consider that .02 mm is only .00078 inches. People shoot .223 ammo out of 5.56 chambers every day. 5.56=.2189 inches. Point is very few things work out to be exact when it comes to ammo.

  58. Vicky on said:

    Good one…..simple to understand

  59. Albert on said:

    What size ammo does a winchester 30×30 shoot? Is 308 the same as a 30×30.
    Waht pistol ammo can you shoot through a winchester 97a.

  60. ron delatrinidad on said:

    can a .25 cartridge be a substitute for an 8mm cartridge?

    • A Gun Guy on said:

      Ron, are you talking about a .25 ACP pistol round? The only 8mm rounds I’m familiar with are rifle rounds. So, if the .25 ACP is what your referring to, you could not substitute one for the other. They are VERY different types of ammo. Not to mention the fact that the 8mm is much larger than a .25. 8mm is almost 0.32 of an inch.

  61. funtogo on said:

    The .17 ..can this used in a 22 cal revolver ?

    • A Gun Guy on said:

      No, you can’t interchange ammunition from one firearm to another without adapters.

        • James McHenry on said:

          A couple things you CAN change, depending on the strength/length of the cylinder of a revolver:
          .357 mag / .38 special
          10mm / .40 S&W
          .45 Long Colt / .45 ACP

          The general rule is, if it is made for the first, you can use the 2nd as a cheaper alternative. ALWAYS CHECK WITH THE MANUFACTURER.

          • King Dude on said:

            Don’t forget

            9mm / .380

  62. G. L. R. on said:

    gracias senor, very good!!!!

    • A Gun Guy on said:

      very happy to help

  63. USMC on said:

    I never go to Wikipedia it sux

  64. JeffreyB on said:

    Thanks, Gun Guy…..You laid this out in a very simple way that helped me explain this to my son…JUST what I was looking for when he asked why a .22 was so much smaller that a 9mm

    Really, S.J.B…? …REALLY?!?!?

    • A Gun Guy on said:

      Glad to be of help, JeffreyB. That’s what I hoped to do when I started this site, so it makes me happy to know I’ve been helpful.

  65. stan on said:

    why is a .380 smaller than a .38 and why would either one be any different than a .380000

    • A Gun Guy on said:

      Good question, Stan. Actually the .380 and .38 special have nearly the same diameter. The big difference between the two rounds is not the slug itself but rather the bullet casing. The length of the case for the .380 is almost half that of the .38 special. So, the load is much hotter providing more velocity. Here’s a great article outlining the differences in more detail: http://gundata.org/blog/post/38-special-vs-380-acp/

      Hope that helps.

  66. S.J.B. on said:

    According to Wikipedia, caliber is decided from the internal measurement of the barrel across the lands. The evidence for this is that a 9mm bullet is in fact not 9mm but 9.02 mm, so to my mind your article is misleading.

    • A Gun Guy on said:

      Well, (a) “misleading” is an inaccurate criticism. This article is about “bullet caliber” not “firearm caliber”. If I was discussing what caliber is when describing specific firearms, then I would say that it refers to the inside diameter of the bore. But I’m explaining here how to understand the difference in caliber in relation to ammunition.

      (b) If you’re number one source of information is Wikipedia, prepare yourself to be mislead often. Wikipedia is a great resource, but not always 100% accurate.

      • Robin on said:

        Well said Gun Guy! I’m a woman and I’m going to purchase my first hand gun tomorrow for self defense and home protection. The way you explained the caliber and size of the ammo will really help me with choosing the right firearm for me. Been doing a lot of research and I may go with the Ruger SR9 and/or the S&W Bodyguard 38.

    • TALC on said:

      Also there is rifling and the inside of a barrel and that closes .02mm of space betwen the bullet and the inner edge of the barrel.

    • mik3 on said:

      SJB I agree, caliber is measured across the lands of the barrel. Bullet diameter, what the writer calls bullet caliber is sometimes not the same as the actual caliber. The writer should have explained this difference in the article.
      Example: a .38 caliber bullet is designed for a .357 caliber firearm. the manufacturer calls the firearm a ’38 caliber’, the actual caliber of the firearm and bullet is .357″.
      Confused? Don’t be. In 1963 two Dallas detectives identified a rifle as a 7.62 Mauser by reading the barrel, the rest is history.

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