If you remember Spielberg’s masterpiece Jaws, Robert Shaw played Quint the seasoned shark hunter. He used a Greener Whaling harpoon gun in the movie.
Here is a video of a guy showing off his Greener Whaling harpoon gun. The Greener harpoon gun uses a martini action and they made a lot of 12 ga shotguns with the same action.
Here is a scene from Jaws where Quint gets the harpoon gun out.