Factual error: When Cagney surprises Ward Bond in a saloon, they run out the back and across a rail freight yard. They jump onto boxcars of a slow moving train. Bond jumps up between two older wooden-bodied boxcars, A and B. Cagney, in pursuit, jumps up between cars B and C. In the wide shots, car C is seen to be a steel-bodied boxcar built at the earliest in the late 1930's. Events in the movie show the time-line to be set in September, 1893.
Continuity mistake: Cagney and Ward Bond have a shootout while hiding at the opposite ends of the same moving boxcar. Early in the shooting sequence, Bond fires his gun frame right towards Cagney at the far end of the car and the muzzle flash from the blank round incidentally burns the surface of the wooden trim at the corner of the car. It is quite a large distinctive shaped burn, readily visible on the surface of the car occupying the right side of the frame. However the burn is also visible in all of Cagney's camera shots, still on the car in the right side of the frame, now behind Cagney as he fires frame left. Obviously, the two actors were photographed each taking all of their gun-shots in two sequences, using the space between the same two cars, one firing left, the other firing right. No camera move. Minimal lighting change.