The comparison weighs mounting weight, barrel length, muzzle velocity, range, shell size, and rate of fire rather than treating calibre alone as decisive. The 5.5-inch weapon fired an 85-pound shell and could reach about twelve rounds per minute with a capable crew, nearly twice the practical rate quoted for the six-inch gun. For a roughly 5,000-ton First World War cruiser or a large destroyer, it could therefore offer an attractive balance of hitting power and handling. The six-inch gun endured because it became the accepted light-cruiser maximum and its weight mattered less on later 8,000- to 10,000-ton ships.
Chapter · 49:05-53:27
The 5.5-inch versus six-inch cruiser-gun tradeoff
The lighter 5.5-inch gun offered nearly double the practical rate of fire, while the six-inch weapon gained staying power as cruiser size and treaty definitions changed.