The Gatling gun that McClintock carries weighs over 170lbs or 77kgs without ammunition. It is impossible for a horse to carry a full grown adult, saddle and equipment as well as such a gun. Gatling guns were in effect artillery pieces served by a four man crew and usually transported by several animals along with a gun carriage or tripod.
A Gatling gun of that era weighed 170 pounds. It could not be picked up with one hand and mounted on your saddle.
Eli's words "I did" while stabbing a character are obviously dubbed.
There is talk about taking some cattle to Alberta. The series is set in the 1880s-90s. Alberta did not exist until 1905. Prior to that, it was part of the North-West Territories.
Thomas picks up his knife stuck in the ground but it makes the sound of metal upon metal, not of soil being displaced.