Why a short 16.25-inch gun wasted its apparent size

Why was the 16.25-inch 30-calibre gun unsuccessful?

It was heavy and complicated, but its short barrel did not give such a large shell enough length to achieve worthwhile performance.

The gun combined great weight and mechanical complexity with a short 30-calibre barrel. A very large projectile still needs enough barrel length for propellant gases to accelerate it effectively. Proportions that may be tolerable on smaller weapons become increasingly limiting as calibre grows. The result was much of the weight and complexity of a giant weapon without a matching ballistic advantage.