The Armalite M16 found by police at Port Arthur yesterday is an American military-style semi-automatic or fully-automatic weapon completely banned from import into Australia.
It was banned in 1987 after a metting of State and Territory police ministers.
A director of Gun Safe Tasmania, Graeme Norris, said the weapon fired a .223 bullet which had a bigger-than-usual cartridge.
"It fires bullets at 3000 feet a second rather than the conventional speed of 1300 feet a second, and was designed to kill people and animals," he said.
Mr Norris said there were probably many of them in Australia before the ban was announced.
He said they were a very expensive weapon to buy.