When Mr. Holtz heads for the Indian camp there are 16 riders who stop for water. Mrs. Holtz shoots one of them on the way, and seven more are killed during the gunfight, including Mr. Holtz. And yet, at the end of the film there are still16 riders shown riding away back to town.
The film, which we are told is set in 1862, shows Christopher Reeve's character using a Gatling Gun. This gun was only designed in 1861, and patented in 1862. It did not enter Union Army use until 1866, and was certainly not available in Texas in 1862.
Britt, when talking to Running Dog, refers to the guns the Indians bought as Flintlocks. However, the guns the Indians bought were in fact percussion locks. These men would have known the difference.