He may have made his choice based on being issued an 1860 during the Civil War. I would imagine a lot of US purchased Colt Army models wound up in civilian hands by 1876 when Hickok was still using the 1851 Navy. More history speculation.....
No need to speculate.
Following is a summary of guns Hickok is known to have owned:
- 1847–56: Hickok hunted game with a flint or percussion lock shotgun.
- 1857: Old-timers in Johnson County, Kan., recalled that with a .44-caliber Colt Dragoon revolver, young Hickok could hit an oyster can at 100 yards.
- 1861–65: Photographic and documentary evidence indicates that Hickok was armed with one or a pair of .36-caliber Colt Navy revolvers, worn butt-forward in open-top holsters.
- 1867: Henry M. Stanley was the first to publish a reference to Hickok’s recently acquired pair of ivory-handled Navies.
- 1868–69: Wilbur Blakeslee of Mendota, Ill., photographed Hickok in March 1869 dressed in buckskins and carrying the above pistols thrust into a U.S. cavalry belt alongside a large butcher knife.
- 1869–73: The Navies remained prominent at Abilene and when he joined Buffalo Bill’s Combination theater troupe in September 1873.
- 1874: When Hickok left Cody at Rochester, N.Y., to return West, Cody and partner Texas Jack Omohundro presented Wild Bill with a pair of .44-caliber Smith & Wesson No. 3 American revolvers later said to be almost as accurate as a rifle. No further reference to them has surfaced.
- 1875–76: Reliable sources suggest that Hickok carried a pair of .38-caliber Colt Navy revolvers converted from percussion to accept either rim- or center-fire metallic cartridges.
- 1876: Wild Bill was buried with his prized sporting version of the .50-caliber Springfield Model 1870 rifle at his side.
- 1879: When Wild Bill was reburied on Mount Moriah, someone spirited the Springfield from his coffin. The rifle passed through a number of hands before landing in the James Earle collection.