The Golden Gun
Although The Man With The Golden Gun was less than memorable, the Golden Gun will go down in Bond history as one of the best gadgets of the series. A gun that can be collapsed into a lighter, a pen, and a cigarette case; only in a Bond film. The gun, used by Scaramanga, brought about the death of numerous unsuspecting men and women including Bond's love interest. Since it is not an actual gun, no specs or reviews are available.
In Ian Fleming's The Man With The Golden Gun he described the gun as "gold-plated, long-barrelled, single-action Colt .45. ....special bullets with a heavy, soft (24 ct.) gold
core jacketed with silver and cross-cut at the tip, on the dum-dum principle, for maximum wounding effect."
Thanks to Alex K for the Fleming info