Archaeologists have discovered America's first firearm that was used by explorers searching for the 'Seven Cities of Gold' nearly 500 years ago.The bronze cannon, or wall gun, was part of the Coronado expedition led by Spanish conquistador Francisco Vázquez de Coronado, who traveled to the New World searching for a fabled city filled with treasures.The 40-pound weapon was designed to fire round projectiles, or buckshot, which would attacked enemies like 'a swarm of hornets.'The team conducted a radiocarbon analysis on the artifact, finding it was fashioned between 1500 and 1520 with metal that indicated it was cast in Mexico due...