Does gun prove Portuguese discovery of Australia?

In 2010, a family discovered an antique gun buried in the sand on Dundee Beach in Australia's Northern Territory. The artifact, which resembles a 16th century swivel gun, has revived the theory that the continent was discovered by Portuguese seafarer Cristovao de Mendonca in 1521. (photo)

"I have no doubt the Portuguese went as far as Darwin, so finding a gun off a beach near Darwin wouldn't surprise me at all," said author Peter Trickett, who believes that Australia appears on a 1547 map by Nicholas Vallard as Jave la Grande.