This is the Black version of the 12" Barrel .45 Caliber Revolver designed by Samuel Colt , USA 1873. It is known as "Single Action Army" and was used by the U.S. Army and possibly the first reliable handgun of history. It has the has been given any nicknames, including "Frontier" and "Widowmaker".
It was manufactured with different barrel lengths:
The "Buntline Special" was used by the Legendary Wyatt Earp and became the most popular gun in the Old West.
Roosevelt had one engraved with his intials and George S Patton used two.