Why an unrestricted gun race might revive mixed batteries

Would barrel wear and muzzle-velocity limits impose a practical ceiling on battleship gun calibre?

Yes. A race beyond 18 inches could revive mixed batteries, with faster 13.5-inch guns exploiting damage caused by the heaviest shells.

Very large railway guns show how higher muzzle velocity and extreme calibre can produce severe barrel wear. An unrestricted naval gun race might push beyond 18 inches until practical experience exposes the largest weapons' slow fire and short barrel life. That problem could revive a pre-dreadnought pattern: paired 18-inch guns, faster 13.5-inch weapons, and smaller batteries against destroyers. The heaviest shells would damage armour designed to resist them. Repeated 13.5-inch fire could then exploit the weakened area with a better chance of landing the next hit nearby. The idea is tactically intriguing, although the resulting ship would be enormous and might require wider Panama and Suez canals.