From Halopedia, the Halo wiki
A revolver contains a barrel, with a revolving cylinder of ammunition.
On October 28, 2558; Fleet Admiral Terrence Hood held a revolver as his service pistol. According to Admiral Serin Osman when she saw Hood holding this revolver in his hand in the halls of HIGHCOM Facility Bravo-6, it was considered an odd sight that made her nervous.
Petra Janecek's revolver
Non-canon and dubious canon appearances
List of appearances