The main character shoots 11 rounds from his 6 shot revolver, reloads, shoots 10 more rounds, reloads, and shoots 10 more rounds. At other times during the film, he has to reload after 6 shots, especially when cornered by zombies.
The saloon door in the first town is made of modern plywood that didn't exist in 1849
Several characters are obviously wearing modern boots and shoes with fancy rubber soles and modern Levis.