• Dr. Coomer@lemmy.world
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      9 months ago

      Maybe the original was 5.56mm and some dumbass decide “nah, not enough b u l l e t, better make it 5.7mm.”

    • alcoholicorn@lemmy.ml
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      9 months ago

      556 was the measure of the inner diameter of the rifling of a barrel of a gun that shot 556.

      Metric is confusing. That’s why for most shotguns, we measure the width by the number of lead spheres of that diameter that would equal one lb, eg a 12 gauge shotgun is the diameter of a 1/12lb sphere of lead.

      Nobody knows how big 18.53 mm is, but everyone knows what a 12 gauge shell looks like.

      Oh, and gun powder is measured in grains, maybe early smokeless pellets were about the same size as grains of wheat.

        • John_McMurray@lemmy.world
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          9 months ago

          he’s serious. The old casting method for round shot was to dump a measured amount of molten lead from a tower into a pool of water 40 feet below. the molten lead would form a sphere in free fall and fully set in the water, so it was convenient to define gauge diameter by fractional weight of a pound. Twelfth pound sphere fits a 12 gauge gun, etc.