Why Britain might accept a lighter 18-inch shell

Why might Britain use a relatively light shell in an 18-inch gun?

A lighter shell is easier to handle quickly, potentially raising the rate of fire enough to help a six-gun ship compete with eight-gun opponents.

The British 18-inch shell appears light beside later Japanese and American heavy-projectile concepts. It was a first-generation design that could be improved, not proof that the gun lacked power. Lower projectile weight also eases movement through magazines, hoists, and loading machinery. On a ship with six rather than eight guns, a higher practical rate of fire could partly offset the smaller broadside while each hit remained devastating.