Why Britain preferred 4.5-inch to 4.7-inch dual-purpose guns

Why did the Royal Navy move from 4.7-inch to 4.5-inch dual-purpose guns?

The lighter 4.5-inch ammunition was easier to handle and could sustain a slightly higher practical rate of fire.

The move from 4.7 inches to 4.5 inches was driven chiefly by rate of fire and ammunition handling. A 113 mm round was fractionally easier for crews to move repeatedly than a 120 mm round. That small difference accumulated during sustained loading, especially when a dual-purpose weapon had to engage aircraft. The choice was therefore a practical human-factors compromise rather than a judgment that the larger caliber lacked hitting power.