"You have the No 1 disappearing gun in the world," Mr Wilson said this week.
The city's former coastal defence gun was the only Armstrong disappearing gun which still worked by retracting as intended, Mr Wilson said.
The Dunedin gun, installed about 1889, after fears of a Russian naval attack, was part of Dunedin's "Fort Taiaroa" defences.
The weapon was designed to "disappear" by dropping into the relative safety of a gun emplacement for reloading.
Mr Wilson (75), who lives near Newcastle, England, gives historical talks and is a guide at Cragside, the former country home of 19th-century Newcastle inventor, industrialist and philanthropist, Lord William Armstrong, whose firm built the gun which bears his name.
During a family holiday in New Zealand, Mr Wilson this week made his first trip to Dunedin, specifically to see the gun, which has been painstakingly restored as part of an historic exhibition co-ordinated by the Otago Peninsula Trust.
He also gave a talk in the city about Lord Armstrong, by arrangement with the trust's Fort Taiaroa committee.
Lord Armstrong (1810-1900) was "an amazing man": a lawyer, as well as a scientist, engineer and inventor, who had contributed strongly to Britain's industrial revolution, through many inventions such as dockside hydraulic cranes and through hydraulically controlled bridges, including Tower Bridge, London.
Committee member Laurie Stewart said it had been good to meet Mr Wilson and learn more about Lord Armstrong's life.
Mr Wilson said he had wanted to visit Dunedin after a volunteer helper at Cragside had visited the city several years ago and, on returning to England, had handed over a brochure with an item about the gun.
