In the bar where Sabata and Ballantine meet and they start to play the piano. When Sabata walks to the piano, he lays his gun on the table. In the wide shot of both playing the piano, the gun is missing from the table.
At 58:54 Sabata slides down a rope using both hands. No weapon is visible. As Sabata nears the ground, he is using his left hand to grip the rope, holding his rifle in his right hand.
A man being executed by firing squad would not be allowed to hold a book.
AT about 20 minutes, One of the rebels said, "Sabata is in Kingsville TX." The movie is set in 1867, but Kingsville was established in 1904.
When Sabata invades Colonel Skimmel's quarters, he sees the reflection of a person hiding behind the door. The person in the reflection is not Hertz.