Anonymous
Anonymous asked in SportsOutdoor RecreationHunting · 1 decade ago

what is the difference between caliber and mm?

what is the difference between caliber and mm becuase some bullets are 9mm and others are 50 caliber so what is the difference and we do they use different types

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  • 1 decade ago
    Best Answer

    Caliber is measured in inches. 50 caliber is .50 inches or half inch diameter ball. Why two systems? You could ask why the USA never converted to the metric system. Of course the pat answer is it would have been so expensive to retool. Fifty years later, what's the excuse now? There are 25.4 millimeters in an inch. That makes the 50 caliber 12.7 millimeters.

  • 1 decade ago

    Caliber is measured in so-many parts of an inch. For example, a 357 Magnum is .357 (three hundred fifty seven thousandths of an inch, bore diameter). Millimeters are metric. So a 9mm is a 9mm bore diameter. However, it's an old and complicated process, and sometimes it's totally illogical. For instance, a 38 caliber, is actually .357 bore diameter. That's why you can shoot 38's in a 357. They made the 357 round longer so it couldn't fit into traditional 38's. It would blow them up because it's a much more powerful round. The 38's, being less powerful, won't harm a 357. And the 38 got its designation in the first place because of the changeover to smokeless powder from the traditional black powder. In black powder days, the most popular revolver was the 36 caliber, which is what .357 is when rounded to the nearest hundredth. But when the world changed from black powder to smokeless, a new designation had to be found for the new, more powerful guns, so they bumped the caliber up to 38 (in theory at least), although in reality, nothing changed but the name. The bore diameter remained .357. I know it's confusing, but that's the way things are sometimes. Anyway, the basic rule of thumb is that they both measure bore diameter, caliber in inches (or fractions thereof) and mm in metrics.

  • Anonymous
    1 decade ago

    There's really no difference whether you use Imperial or metric measurements. Cartridges developed in Europe routinely use metric measurements, with 5.56mm, 6mm, 6.5mm, 7mm, 8mm, 9mm and 9.3mm being popular sizes. An exception is the 30R Blaser. On either side of the ocean, pretty well everybody knows that 308 Win and 7,62x51 are the same cartridge. Most of the classic British and American cartridges use Imperial measures, but there are a lot more exceptions in that direction. Also, CIP gives metric nomenclature, and the cartridge boxes are so labelled, for cartridges that originally had Imperial designators, a sensible thing to do since the rest of the world simply aren't familiar with inches.

  • 1 decade ago

    Ignore most of the answers because they are wrong. 9mm IS a caliber. Caliber is either in imperial units (inches) OR metric units. Caliber DOES NOT imply inches. This is an assumption made by many, just like the boneheaded assumption that a .38 Spl actually measures .38 at the base of the slug.

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  • Anonymous
    1 decade ago

    Caliber is english. MM is metric.

    50 caliber is about 1/3 larger than a 9mm.

  • 1 decade ago

    The above answers are correct. But to answer your last question, MM is metric and is the standard for most of the world. Caliber is American/British standard. Both measure the same thing- the inside diameter of the barrel or bore diameter. Ammo developed in Europe is name as "X" mm e.g. 9MM and ammo developed in America and Brittian is name by its caliber e.g. 45 colt.

    A universal standard of using metrics has been adopted by the NATO for military purposes.

  • 1 decade ago

    Caliber is a designation and can be in metric or inches. .308 is the same as 7.62 /// .308 inches or 7.62 millimeters. 9mm is same as .38. Just get a conversion table or go with the flow.

  • 1 decade ago

    MM WOULD BE A CALIBER, IN OTHER WORDS "I HAVE A 9MM GLOCK 9MM IS THE CALIBER, IF IT WERE A 357 MAG. 357MAG IS THE CALIBER OR SIZE OF THE ROUND{BULLET}.

  • 1 decade ago

    There is no difference in either. It is a different term in measurement in the bullet. Meteric vs. calibration.

    Source(s): Spoke to a gun enthusiast.
  • 1 decade ago

    9mm is 9 milimeters

    .45 cal means meassured in inches

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