The .45 automatic or Colt M1911 was a semi-automatic pistol used on Earth. Calvin Sutherland owned a .45 Colt pistol. (TOS novel: From History's Shadow) When Julian Bashir, Miles O'Brien and others were thinking of ways to remove Frank Chalmers from the Vic Fontaine holosuite program, O'Brien realized that if they chose to shoot Chalmers, they would have to do so by using a period specific weapon like a .45 pistol. (DS9 episode: "Badda-Bing, Badda-Bang")