At the court scene (00:30:10), William Holden's character makes the same movement twice in consecutive shots whilst getting off the chair.
When Johnny Howard pays the bartender with gold dust, the bartender weighs it with scales, but he pours the gold into the scale until it goes all the way down. The correct way to do it is to put the correct scale weight on one side and then pour the gold slowly into the other side until the scales are balanced.
Many of the men are wearing trousers with belt loops and belts. Belt loops were not added to men's trousers until the 20th century.
Shown was the Remington 1875 revolver. The Civil War ended in 1865 so this revolver was not even invented.