• alcoholicorn@lemmy.ml
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      3 个月前

      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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        3 个月前

        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.