Factual error: When Gene Hackman is shot at the end he looks down and sees the hole in his shadow. However if he was shot from someone at the same level as him, the hole would be straight, parallel to the Earth's surface. So if he could he the reasonably proportioned shadow the angle of the sun wouldn't show any hole in him at all.
Suggested correction: First, it is reasonable to assume that Hackman is significantly taller than Stone, and, given that she is firing from a hip draw the angle of entry for the fatal gunshot would be on a upward trajectory. This generally upward bullet trace combined with the evening or late day sun could be reasonably expected to cast a shadow if you suspend disbelief initially to allow that this type of wound is practically plausible.
The fact that she is shorter is irrelevant given the distance between them. For the angle of the light showing through him to make sense (and that's assuming it makes sense for it to show through him at all) she would need to be kneeling directly in front of him. The fact that, as you say, suspension of belief is required demonstrates the original mistake is valid.
Suggested correction: He doesn't see the hole in his shadow. We see him look downward slightly, then we see the shadow slightly from the side, not the view he would see. We then see him looking down at himself. It's easy to assume he is looking at his shadow, but we don't see him doing that. He could simply be staring into space, with the shadow presented for dramatic effect for the viewer.
Factual error: In two, maybe three scenes, there are ring-necked pheasants. One is early in the movie as the Jameses ride past a butcher shop where ducks and pheasants are hanging up for sale. One is mid-way in the movie in the scene of the house- or barn-raising and big picnic. The movie supposedly took place in the mid-1870s. Pheasants were not imported to America from China until 1881.
Factual error: In the movie, Wild Bill has a shootout with the bad guys in the stables. He is holding two colt revolvers, each having the capability of holding six rounds each. However as a safety precaution, only five rounds were loaded in the revolver with the hammer resting on an empty chamber as a safety. Therefore, he could only have ten rounds total from the two colt revolvers. He fired far more than ten rounds without reloading.