In describing his rifle to Marsden, Quigley says it is a "lever action." Actually, it has a falling-block action. Pulling the lever forward opens the breech and ejects the spent cartridge case. The new cartridge is then inserted manually, as Quigley is seen doing many times, and the lever pulled back, closing the breech.
In the distant shot of Quigley tying his bandanna around his wounded leg as the soldiers ride away in the distance, the sun is just about to set behind a hill. Just before and after that shot, the shadow of his hat falling on his face and shoulders shows that the sun is high overhead. In addition, there should be three dead men on the ground -- Marston, the Scotsman, and the Kid - but only two are visible and in different positions.
When Quigley shoots the bucket to prove his marksmanship to Marsden, the vernier sight is at different settings during the three shots fired. First in the middle. Second shot (close-up) shows at bottom. Last shot shows somewhere above middle. At the distance he is shooting, it should be at or near the top causing the end of the barrel to rise making the bullet follow an arc to the target.
While the dingoes are advancing on Cora and the baby in the cave, and she is reloading the revolver and, the right shoulder strap on her blouse keeps falling down, and then reappears on her shoulder in the proper place all by itself.
When Quigley kills the man after they are dumped in the desert, there is a drastic difference between the shadow on the dead man's face between the moments just before Quigley shoots and after he shoots.
While the rifle used by Quigley fires a supersonic round, it decelerates quickly. At ranges less than 300-400 yards, the bullet would arrive sooner than the "bang", but only by a fraction of a second. At ranges greater than this, the sound of the shot would arrive before the bullet. Thus, there would never be a point where the sound of the shot would follow the bullet by several seconds.
Quigley and Crazy Cora are taken to a camp by the native Aboriginal people. There they chant and play a Didgeridoo. In this part of Australia, Western and Central there are no didgeridoos. The Yirdaki and Mago Didgeridoo are endemic to only Arnhem Land. In the Western part they use Mago, in the North East part they use Yirdaki. This is at the very northern part of Australia, in a small delimited area. When this scene was cited to have taken place none of the the central and western Aboriginal Australians, namely in the desert, used a Didgeridoo in playing music. Only in later times has it spread more though out Australia.
When goodliest talking to the man who's trying to find something for him and tells him he "could use a good horse", the man replies that he's a man from the "land of the free and the home of the brave". The USA's current national anthem wasn't adopted until 1931. Is very unlikely that an Australian would know that line in association with with an American during that time period.
When Quigley arrives at Marston's ranch and Marston is looking at the paper with the bullet holes through it, the holes have been cleanly cut by the bullet. In fact, round nosed bullets such as the type Quigley's rifle uses leave ragged holes when shot through paper, especially at 900 yards. Only bullets with a sharp shoulder made for shooting paper targets will leave a clean hole.
When Crazy Cora passes out in the desert and falls forward, she puts her hands out at the last moment to break her fall. In reality, when a person loses consciousness, it's impossible to put ones hands or arms out to lessen the impact of the fall like this (although it is very difficult to fake this type of fall without some form of involuntary movement to soften the effects).
In the close-ups with the sun overhead, and the shadow of his hat falling on his face and shoulders, there is a second shadow of the brim of the hat on his forehead, revealing the presence of another light source.