Why a 15-inch gun does not have one simple cooling time

How long did a British 15-inch gun take to cast and cool?

No precise duration is given. Manufacture involved repeated heating and cooling cycles rather than one cooldown.

No precise duration is given for casting and cooling a British 15-inch gun. The manufacturing process involved several cycles of heating and cooling rather than one uninterrupted cooldown, so the answer depends on which stage the question is measuring. This rejects an oversimplified single-time estimate while preserving the limits of the recollection.