Just looked at the movie again & paused it at the scenes were the British rifles are shown. They definately aren't Sniders as there's no breech loading mechanism, though you'd think by post 1874 (based on Quigley using an M.1874 Sharps) they would have been using them, so must be some variety of Enfield Cavalry Carbine, as guessed at above, as they have a saddle ring & bar on the side.....definately not Musketoons which were designed for use by the Artillery.