Rollin White single shot pistol.
Circa 1860: 32 caliber rimfire single shot pistol.
This gun was designed by Rollin White whose 1855 patent on the bored-through cylinder had a huge impact on the history of American firearms. Smith and Wesson bought the patent and effectively prevented Samuel Colt's company from developing cartridge revolvers until after 1870, when the Rollin White patent expired. Ironically this Rollin White pistol violated the patent he sold to Smith and Wesson, so Smith and Wesson sued him and forced him out of business.