• 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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          8 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.

            • John_McMurray@lemmy.world
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              8 months ago

              Here’s where it gets political. I learned about shot towers in passing years ago and thought that was a good idea. You learned about shot towers in passing, but then with a detailed explanation, still thought that was ridiculous. One of us is prone to rational thought and the other is not. This is a 17th century conversation happening now.

              • drathvedro@lemm.ee
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                8 months ago

                Ah no, it’s just that from reading this, I imagined it being poured outside, not inside the tower.

                Like, someone looking at Galileo doing his experiments dropping weights off Pisa tower, and saying:

                — What if we put a bucket underneath? What a splash it’d make!

                And another one going:

                — Yeah! And why just weights, let’s throw molten lead off! What safety concerns? Haven’t heard any

            • John_McMurray@lemmy.world
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              8 months ago

              No problem. There’s always a reason, and usually a pretty interesting one, for old odd hold overs like this, but it’s been 200 years since shot towers were a thing, only history buffs and muzzleloader enthusiasts really know about these.

      • Everythingispenguins@lemmy.world
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        9 months ago

        Grains as a measure of weight comes from the Troy weight system, think Troy ounce of gold. It is a very old system that for a long time was mostly used by apothecaries and probably has its origins in Ancient Rome.

        • bluewing@lemm.ee
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          8 months ago

          Grains Apothecary is used to measure powder charge weight is because it was a “fine” enough scale for measuring small amounts of things that if you get it even a tiny bit wrong, can kill you. So, ammunition manufacturer’s looked around and scales used for accurately measuring small amounts of drugs were commonly available, so they went with that.

          Cool side point: Powder charges are checked by weight and dosed out, (or thrown), by volume as it has always been done since the first gonnes were a thing.

    • 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

        OK, so there is a 5.7mm, that’s the same diameter as 5.56/.223, but it’s not compatible with either because of the french.

          • alcoholicorn@lemmy.ml
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            9 months ago

            Kinda?

            The case is both shorter and narrower than 556/223, so it won’t even sit right in anything not designed for it. But FN makes quite a few guns that use it.