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How were early cannon classified by the weight of the ball they fired?

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Early artillery founders adopted the practice of classifying cannon based on the weight of the solid projectile they were designed to fire. Under this system, a gun was designated by the weight of its ammunition; for example, a "12-pounder" was a piece bored specifically to fire a 12-pound cannonball.12

This method of nomenclature remained standard for centuries, as ordnance was categorized by the weight of the solid cast-iron ball it fired. However, this classification system was eventually abandoned in the latter half of the 19th century. As technology advanced, the adoption of cylindrical and elongated projectiles—which weighed more than spheres of the same diameter—rendered weight-based designations impractical. Consequently, artillery classification shifted to measuring the calibre of the bore in inches or millimetres.3