Why did we end up with a calibre of 5.56 mm (and others with 5.45 or 5.82 mm)? The understanding of modern infantry firearms calibres requires in part an understanding of their history.

The typical European 18th century service long firearm was a musket. The calibres were astonishingly large, and the typical bullet was actually a spherical ball. Cartridges were introduced, typically paper with ball and blackpowder, and de-mixing of the blackpowder over time was an issue.

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