When Jim and Artie drop off Lonie and swing the juggernaut around, the headlamps are off in one shot, but the camera cuts to another shot instantly and the lamps are on.
When West first rides up to the County Clerk's office, he ties his horse to the near end of the hitching post (closer to the office door). When he leaves, his horse is tied up to the other end (further from the door) of the post.
The stand-in for Ross Martin, necessary because Martin's leg was broken in real life, is noticeably heavier than the actor in his few brief walking scenes at the beginning before the character's leg is broken.
When the juggernaut breaks up the meeting of farmers that West is attending, in one short scene, the juggernaut is shown backing up. While backing up, the smoke from the smokestack is shown going INTO the smokestack, indicating the scene was shown in reverse.
When West first rides up to the County Clerk's office, he ties his horse to a hitching post which wobbles noticeably as he wraps the reins around it. The outline of the square base the post is attached to is also visible in the dirt.
When the Juggernaut first appears in the introduction scene, the headlights appear to be aimed independently - based on how they shine in West's eyes (from the point of view of the Juggernaut itself), but in the shots of the front of the machine, they are mounted to fixed points, and could not have been aimed in the manner they were. Obviously, independent spotlights were used to create the spots of light.
Early in the program as Jim crosses the street during daylight hours, he casts 4 shadows.
The Gatling gun was fired very quickly, that means the barrels would have been very hot. Yet the shooter wrapped his arm around them with out and signs of being burned. He also tested his hand on them with the same result.
Also the rate of fire of the Gatling gun and the sound of the bullets are much different.
Starting at 41:20, 9 of Bock's men are out in the open at very close range (appears to be ~25 ft) and are fired upon by 8 men with rifles around and in the barn. There is lots of shooting, but not one person or horse is hit.
The escape from the barn at 36 minutes. They are several things wrong about it. Starting with the anchor fired into the wall. What generated that much force. Then how did the wench have enough power to bend pipe. Then how did the anchor hold. It did not go very deep. Wood would have split before pipe would have bent.
After the fight at the General Store, West returns to the train, where Gordon demonstrates the little blue explosive. When he puts it in the flame, it explodes, and actually extinguishes the burner flame. Neither one of the characters does anything to shut the burner off, which would have begun to fill the train car with gas. Gordon should have immediately shut it off to prevent that occurrence.
When the juggernaut approaches the barn, Jim opens the hatch so that he can deliver Lonie to the farmers. As soon as he sticks his head out, stop firing when they see it is Jim. BUT so do the bad guys. When Jim helps Lonie out, they would have seen that the man getting was not one of them. They also would have recognized Lonie and known that she would have had no business being in the juggernaut. Further, they would have had to have recognized Jim and realized that he was there to foil their plan. Therefore, they would have not stopped shooting at Jim as he got out of the Juggernaut, particularly as he would made a great target on the top of the Juggernaut.