Why was iron a plausible material for early naval shot?

Did early naval cannon use iron shot or another material?

The initial answer tentatively favours iron because it combines strength, useful weight, and affordable cost.

The initial suggestion is that early naval cannon probably used iron shot. Iron combines sufficient strength with enough weight to cause damage and a cost low enough to expend in firing. Brass is mentioned as a possible experimental material, although its expense would count against it. This tentative suggestion does not establish the ammunition used by every early naval gun.