At about 1:05, when John Henry rides to the church to pray and talk with his father, he rides up a hill and across the meadow. When he is inside the church, you can clearly see buildings through the open door, where there had been a meadow.
When Chadwick is walking to the outhouse he is walking away from the shooter. Then when he is actually shot it happened with the shooter in front of him. This is physically impossible to be in front of and behind Chadwick within moments.
When John Henry and his father go into town, the shopkeeper with the white apron and gray hair goes down the stairs in front of his store. He then is seen going across the road, then down the stairs again.
30.44 McCurdy is talking to Gentleman Dave outside the saloon and there is a napkin on the finished plate of food in front of McCurdy, at 31.01 again looking towards McCurdy there is no napkin to be seen only for it to appear again at 31.08.
When Frank Tillman is ambushing Mr. Chadwick, Frank is seen taking aim and shooting with his rifle, holding it as a right handed person would. After wounding Mr. Chadwick in the leg and firing another shot that misses, the next shot shows Frank holding the rifle as a left handed person would.
When John Henry goes to buy another gun he chooses the LeMat revolver. The shop keeper remarks that it is 9 shots and a 10 gauge shotgun and places a box of cartridges on the counter. The shotgun barrel on a LeMat is 20 gauge not 10 and it is a cap and ball revolver that does not use cartridges.
Clayton talks about his bad experiences in the Civil War battles of Shiloh and Seven Pines. Shiloh was fought in western Tennessee April 6-7, 1862. Seven Pines was fought in eastern Virginia May 31-June1, 1862. Given that the battles were in different theaters under different commands, it is not possible that he fought in both battles.
The shopkeeper describes the LeMat pistol as having a 10-gauge shotgun shell. The LeMat's shotgun barrel was 20-gauge (or bigger gauge / smaller bore).
When Demi Moore and Kiefer Sutherland are drinking coffee on her porch, the mugs they use appear to be modern polished stainless steel mugs, that were not produced until much later in the mid 1900's.
Hate to be grammar police, but when cleaning the field, Keifer Sutherland's character tells his paw that "Mr. Jenkins came across William and I downriver." The correct grammar would be "William and me."
Generally speaking both pronouns need to match and fit in diction. Therefore if William's name is removed from the sentence, what remains is "Mr. Jenkins came across I downriver," which obviously is poor and incorrect grammar.
When Kiefer Sutherland first arrives home, in the background you can see a field full of round hay bales. Machines to make round hay bales were not available until the mid 1900s.
At the beginning Kiefer Sutherland is chopping down a dead snag, the camera pans to the top of the tree and you can clearly see the tree is dead with no needles on it. When the tree hits the ground, you now see a totally living tree with live green needles right to the top.
Although James McCurdy addresses Reverend Clayton as "Samuel," Donald Sutherland is credited as "Reverend William Clayton" in the closing credits.
At 1:15 after John Henry has purchased his gun, the shop has "Amunition" spelled wrong on the painted wall/sign outside.
Like most westerns, most of the hats shown are incorrect for the period. What is now generally considered a cowboy hat didn't become popular till the very early 1900s.
Winchester 1873 rifles, and Colt 1873 revolvers are seen frequently. The movie was set in 1872, predating the production of these firearms.
When Chadwick is on the ground after being shot in the leg, a small box can be seen under his shirt near his waistline. It is visible after the chest wound also.
(around 1hour 15min) The camera is filming from above, and you can visibly see footprints of modern shoes.
John Henry wields an ax as if he has never chopped wood in his life. The ax is raised over the head, so that the muscles of the back and arms use gravity and momentum to bring the ax down to split the wood. John Henry swings the ax as if it is a baseball bat and it is not an efficient use of the ax.