Bronze is a copper (and tin) alloy, and compared to iron, it has the advantage of having a lower melting point and being softer, making it easier to cast even with lower technology (its disadvantages are that for the same reason, it becomes worn and crooked easily).
But by the 16th century, steel became available, and damascus barrels, made by heating up and forging together steel ribbons with differing carbon content (made by applying stress to the metal by striking), then rolling it around a center stick, and then heating it again and welding it, became widespread. (Through mixing and forging together several types of steel it