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  • Calibres are not “correct”, why?

     Madelyn updated 1 year ago 2 Members · 4 Posts
  • Madelyn

    May 17, 2021 at 8:57 pm

    Hello fellow gun-enthusiasts

    This is really bothering for a while now, and im sure alot of people dont even realise this, but:

    A 5,56mm ( .223 inch Remington) is not 5,56mm but instead its 5,69mm (.224 inch)

    The same with a 9mm which has a diameter of 9,03mm.

    Why is that?

    I would be really glad if someone can clear up why they are named the wrong way and not a single dimension of a 9mm(or 5,56mm) is 9mm (or 5,56mm).

    Thank you very much in advance.

    Greetings from Switzerland.

  • DJRatKing

    May 17, 2021 at 8:57 pm

    The measurement of the caliber’s label is limited to the diameter measured from groove to groove in a rifled barrel. In actuality, the bore diameter is larger than that.
    Edit: Sorry if my post is unclear, English is my second language. But if interested in why this caliber naming convention happens with some rounds, but not others, consider that some manufacturers/developers of firearms measure land to land in the barrel, while others measure groove to groove when determining the naming measurement of the round.

  • MrPibb7781

    May 17, 2021 at 8:57 pm

    Rat King pretty much said it. The reason the bullet is slightly larger than the bore is that it needs to be squeezed down through the barrel to allow the grooves to bite in and impart spin.

  • TheTNPicker

    May 17, 2021 at 8:57 pm

    9mm diameter is .355 99% of the time. Berrys makes .356 for their nines. Why don’t we just call them “three five fives “ instead. Lol

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