In a scene where Charlton Heston and Forrest Tucker mount their horses and take out their rifles, the action is repeated when the camera cuts to a close-up on them.
4 Indians are seen up on the rocks, yet only 3 are shown chasing the rider.
The founders of the Pony Express were not William Cody and James Butler Hickok, but William H. Russell, William B. Waddell and Alexander Majors. Hickok wasn't a rider for the Pony Express, he only worked as a stockman.
Charlton Heston is billed as 'Captain William Frank "Buffalo Bill" Cody'. "Buffalo Bill"'s full name was William Frederick Cody.
Chief Yellow Hand's name is a mistranslation from the Cheyenne. His real name was Yellow Hair, which ironically was an Indian name for George Armstrong Custer.
Buffalo Bill says he sees a Winchester Rifle in an Army soldier's hands. Winchester was not founded until 1865, four years after the Pony Express had stopped operations.
30-year-old Charleton Heston was far too well armed, too old and too tall to play Cody, who was 15 when he rode for the Pony Express. The express riders were small, wiry and went unarmed, to save weight.
When Charlton Heston removes the saddle from his dead horse at the start of the movie, he removes it without undoing the buckle of the cinch that runs underneath the horse. If the cinch was unbuckled, the saddle and the rider would fall off the horse.
Even though a great distance was supposed to have been covered, the same relay stations are used in the initial ride regarding the federal slavery bill.
The setting of the film is the beginning of the Pony Express, which ran from 1860 to 1861. Yet the Californian secessionists who try to stop the Pony Express's first-ever delivery use dynamite, which was not invented until 1867.
The legendary duel between Yellow Hand and Buffalo Bill took place in 1876, sixteen years after the Pony Express was created.
The film is set in 1860, but the handguns all appear to be Colt .45 Peacemakers, which weren't developed until the 1870s.
The time-setting is 1860. The Colt Revolvers shown were Model 1873. Hickok wore Colt 1851 Navy revolvers, which were black powder, fired by percussion caps.
After Cody boards the stage at the start of the movie, Rance pulls out a Remington Over/Under Derringer. The Pony Express operated from 1860 to 1861 and the Remington Over/Under was not manufactured until 1866.
In the final shootout between Cody and one of the main bad guys, the actor's reaction of getting shot doesn't match up with the sound of any gun being fired.
The 4 Indians are shown high up on a rock formation looking down on a valley when the rider goes through at full speed, riding away from them. They are subsequently shown having overtaken the rider. This would not be possible due to the amount of time it would take them to come down off the rocks and get onto their horses.
When Rhonda Fleming's character is walking up the stairs in the hotel (at 26:50), the shadow from the boom mic can be seen on the walls.