When McCord buys the horse and saddle, he hears that Frank Egan had died five years before, in August, 1859, so the time-setting of the movie is 1864. The Winchester lever-action rifle was not invented until 1866.
In one version, there is a jump from a scene where the party of five has stopped for a rest with their horses tied up to a rope, to a scene where the party is seen approaching the town of Tomahawk Gap with the wounded Kid riding the only horse. Three horses have disappeared.