The episode takes place between the end of the US Civil War [1865] and the end Maximillian's rule in Mexico [1867]. Cheyenne and the Mexicans are using repeating rifles, look like Winchesters, in the final battle. The rifles are definitely not Henrys, which first appeared in 1860. They are not 1866 Winchesters, which even if they were, would hardly be in the hands of fighters deep in Mexico less than a year after they were introduced. Rifles are at least 1873's which didn't exist in 1867.