Quote:
Originally Posted by Rugger_can
You sir are confusing Caliber with diameter expressed in millimeters they do not mean the same thing. Caliber is the decimal expression of inches of the internal diameter of a rifled barrel measured from the groves (usually) expressed in the unit Caliber or cl.
The diameter of a .223 Caliber round when expressed in millimeters is 5.56mm. It is not called a 5.56mm Caliber round.
It is a common misunderstanding.
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You sir are confusing the vernacular with a technical notation. Caliber is a unit-less measurement of the bullet diameter, not barrel. The actual barrel of a .223 rifle is larger than .223 inches in order to allow the bullet to travel through it. (Same reason why we don't have 5.97mm to 6.00mm airsoft barrels.)
It is
common to express caliber in imperial measurements, but not required.