Continuity mistake: At the end the nasty man is out of bullets so the Bad girl throws him a bullet from her rifle. He puts the bullet in but fails to revolve the cylinder so of course he loses as you would have to thumb-cock and pull the trigger 3-4 times to get to the live ammo. Dumb, dead desperado.
Revealing mistake: In the final scene as Doc tell Billy good-bye if you look up to the top right hand corner of the screen you can clearly see a jet trail in the blue sky. Certainly not possible in those days. (01:42:20)
Continuity mistake: When Rick Nelson tells Angie Dickinson to throw the plant pot through the window to distract the gunmen who threaten John Wayne he seems to have had a hair cut between scenes as his sideburns are halved by the time he reaches the street and grow again later.
Continuity mistake: There is no way the cow (a Hereford I think) could have given birth to that calf (a Jersey or something like that). [The mom is a mixed-breed BEEF cow, the calf a purebred Jersey DAIRY calf. An amazing feat of animal husbandry.]
Continuity mistake: In the barn dance scene Gideon is doing flips on the sawhorse. His shirt becomes untucked and then retucked between flips.
Factual error: When Bob Ford opens the box under the bed, on top is an issue of "The Jesse James Stories" weekly, which was published from 1901-1903 - fully twenty years after the events of this film. (00:36:10)
Revealing mistake: In the scene out West with the buffalo, notice the car driving in the distant background.
Suggested correction: What is the time code? In the scene with the buffalo stampede there are no cars anywhere.
Continuity mistake: When Jack Twist is chopping wood, right before Joe Aguirre visits him on his horse, he sets up a piece of wood to chop. Jack talks to Joe and when the camera pans out to show him ready to chop again, the piece of wood is gone.
Character mistake: When Vallian prepares to leave the homestead, McKaskell asks him how his chest wound was. Vallian was shot low on the right side, just above the gun-belt, and McKaskell, who removed the bullet, was quite aware of the location.
Revealing mistake: As Jango fires the machine gun, the ammunition chain hanging from it is loaded on both sides, and it doesn't move. Also the belt has different sizes of cartridges in it. (00:45:30)
Other mistake: Bandoleer rounds don't fit any weapon in the show. When Pierce tries the Gatling gun, there is no magazine in it.
Factual error: The cavalry sing Low Bridge (or Fifteen Years On The Erie Canal) as they trek across Texas in 1879. This was written by Thomas S. Allen in 1905 during the time the Erie canal was switched from mule power to engine power. (00:49:00)
Factual error: When the riders are watching the wagon train, in the background you can see a communication tower with conical speakers.
Factual error: Outside the Territory Hotel, during the storm, and once earlier in the movie, the taxi cabs are shown with the modern "flip over" vacancy/hired signs that were not used then.
Continuity mistake: At the start of the train chase Tonto blows the whistle as he passes the bad guy who says "shoot him you idiot". The soldier opens fire with the machine gun and Tonto is suddenly back in front and passing him again. (02:03:35)
Continuity mistake: In the first shot of the dead man hanging form the tree, his head appears to be about 12" from the tree limb. After Mattie climbs up to cut him down, his head is several feet from the tree limb.
Visible crew/equipment: At Lees Ferry when the stagecoach is crossing the river, there is a shot from on top of the stagecoach. As the camera pans over to the river, a clear shadow of the camera and its film magazine are visible.
Other mistake: There's a horse that has apparently ridden up a cliff, and an electrical burning brand that can be changed onto different flame settings.
Continuity mistake: At the beginning, in the scene where Rayne finds two bodies near a small house, she takes out one of her blades. Firstly, she grabs it in a wrong way (the tonfa-like blades should be held under the arm), but when the camera angle changes she holds it properly.
Continuity mistake: A couple of times in the movie, the camera pans to John Wayne, and his hair is parted on the wrong side. (Reverse editing flaw).