Factual error: When the posse arrives at the mission, a horizontal jet stream can be seen during this scene. (01:00:00)
Visible crew/equipment: Not sure if was a crew member but just before they are planning to shoot 5 people Joe runs across the land and there is a guy lying on the ground. It looks like he's lifting his head or something.
Revealing mistake: When Clint Eastwood is shooting his 1896 Mauser Machine pistol, with the long barrel, even though he fires numerous shots the hammer remains fully cocked and does not move.
Other mistake: In the scene where Kidd is in the watchtower getting ready to smash the guy in the head with the water jug. When he lowers it, it looks to be about 3/4 full, but when it smashes the guy in the head, about a cup of water comes out.