Why a ship's guns could outperform the same weapons ashore

Were shore guns more accurate than the same weapons mounted on a ship?

Not necessarily: shore guns were steadier, but ships often had much better and more frequently upgraded fire-control systems.

The comparison is not settled by mounting the same gun on land and at sea. A shore battery has the obvious advantage of a stable foundation. A serving warship, however, was more likely to receive current directors, sensors, and fire-control equipment. Better target acquisition and calculation could outweigh the ship's motion, leaving the naval installation more effective despite its less stable platform.