The real Deaf Smith was neither deaf nor mute, merely hard of hearing.
When men are shot the squibs are obvious beneath their shirts.
The film is set in 1830, but they use Winchester-rifles (constructed 60 years later).
The Gatling gun used is like nothing ever produced. The real Gatling gun wouldn't be invented until the 1860s. It fires cartridge ammunition that wouldn't be invented for decades.
The ONLY revolver available in the 1830's was the Colt Paterson. "Deaf" Smith's revolver shows details 15+ years newer.
In one scene "Deaf" Smith, who is a deaf mute, turns and shoots a rooftop gunman, apparently after hearing the gunman run across the rooftop.