How certain is the distinction between stone shot ashore and iron at sea?

Were the earliest cannonballs stone, and had ships already changed to iron?

Stone shot was used ashore. Iron still seems more likely for the early shipboard supply, but that judgment is uncertain and open to correction.

Stone projectiles were used by early land artillery. The proposed distinction is that ships needed to carry a substantial supply of ammunition and could not count on making more locally. Iron therefore remains the preferred explanation for shipboard use, although stone cannot be excluded. The confidence expressed is about 75 percent, with an explicit willingness to defer to someone more familiar with this period.