Corrected entry: At several points during the film, characters are shown loading brass cartridges into their revolvers. The revolvers shown throughout the film, however, are "cap and ball" models, which were hand loaded and could not be loaded with cartridges. Note the loading levers under the barrels - cartridge revolvers do not have these.
Correction: Cartridge conversions weren't common 'til 1871. Smith and Wesson offered two cartridge revolvers, in .22 and.32, neither of which are portrayed here. The 1860 Henry, predecessor to the Winchester, fired rimfire cartridges, so Carver's rifle is not outrageous. However, all such cartridges were rimfire - Gideon's centerfire cartridges are portrayed a few years prematurely. Carver refers to "shells" - which means artillery projectiles. Any real military man would say "cartridges."
Corrected entry: In the scene where Liam Neeson is crossing the salt flat and falls off his horse. You can see a truck or vehicle pass by in the far background. (01:32:30)
Correction: I have watched the scene where Liam Neeson falls off his horse over and over again, and there is no vehicle or truck far in the background. There is only shimmering light.
Correction: It was common for cap and ball revolvers to be converted to fire cartridges in the time frame of this movie. Cartridge revolvers from the factory were more prevalent after 1873.