Revealing mistake: The gang's visit to Northfield, Minnesota reveals a typical late 18th century town, with dozens of people on many horses and horse drawn wagons. All the horses leave deep tracks in the dirt, because they are walking on freshly laid soil that has not had time to compact. There is absolutely no horse manure to be seen anywhere, despite dozens of horses. Clearly, the film makers used a 20th century town and laid new soil over the pavement shortly before the filming began.
Revealing mistake: In each one of his scenes, every time you see Captain Fuller you can see that the actor is wearing contacts to make his eyes blue. It's obvious contacts with the brown rings of his natural eyes around them. And contacts were not invented for a long long time after this movie takes place.
Revealing mistake: The Giles brother who got "hung" when he fell after getting shot by MacMasters can be seen moving his body (mostly arms). (00:04:06)
Revealing mistake: Stan is using a block and tackle to hoist Ollie up to the balcony of Finn's apartment. When Stan lets go of the rope, Ollie falls and lands flat on his back. It is obvious by the awkward angle of the legs that a dummy was used. In addition, the dummy lands with the legs close together but in the shot that follows, Ollie's legs are far apart and one leg is in the air.
Revealing mistake: When Ransom and Hallie Stoddard are riding the train back to Washington at the end of the film, pay attention to the view out the window as Hallie responds to Ransom's suggestion of returning to Shinbone. When the conductor brings the spittoon and talks to them, the same exterior footage repeats from when Hallie started to speak. (02:01:30 - 02:02:15)
Revealing mistake: When the children stay with the tribe, all of the horses being ridden, although shown having a saddle blanket, actually have saddles under those blankets.
Revealing mistake: When Bud and Wes take competitive turns riding the bull at the presumed high speeds, the bucking patterns and timing aren't consistent. A few times either man goes less than 15 seconds on a mid speed rather than full on bucking. Which even for a practice doesn't add up, and wouldn't fly during a competition.
Revealing mistake: Near the end of the movie, the Bunch are relaxing and passing around a bottle of whiskey. While the actors could not be expected to drink real alcohol, it's too bad the prop guy could not have mixed up some less foamy instant tea, typically used as a substitute in these scenes.
Revealing mistake: When Potter starts shaving at the morning of the Indian attack on the wagon train, his mirror falls off the post, and as he bends down to retrieve it, an arrow embeds itself right above his head. If you look closely in that scene, you can see a length of targeting wire used to guide the arrow sticking to the post above Potter's head. (00:37:10)
Revealing mistake: At the end after the driver of the wagon has fallen off and the horses are running wild you can see a slot in the front of the seat and arms holding the reins.