• borari@lemmy.dbzer0.com
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      2 months ago

      We’re more familiar with 5.56x45mm thanks to all our school shootings thank you very much.

      • alcoholicorn
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        2 months ago

        In the same way a US ton and a metric ton is like 10% different, a 556 bullet is actually 5.7 mm across.

        • Morphit @feddit.uk
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          2 months ago

          Because the minor diameter of the barrel is 5.56 mm and the major diameter is 5.69 mm. If the bullet were smaller than that then the propellant would blow past it. They didn’t make a 'murican millimetre like they did with the imperial system.