Could a battleship combine heavy 18-inch guns with lighter 12- to 14-inch turrets for ranging and anti-raider work?
Short answerNo. Different shell and ranging characteristics make mixed main batteries a fire-control and logistics problem, which dreadnought-style standardization was intended to solve.
NotesA 14-inch shell and an 18-inch shell behave too differently for one to provide reliable ranging information for the other. A battleship would range with one or two turrets that carried the same gun as the rest of its main battery, then bring every turret into the engagement. This is the problem dreadnought standardization solved for long-range fire while also simplifying ammunition supply.