Several times Ash's shotgun acts more like a rifle. This is particularly evident in the windmill, when the Dwarf Ashes fire a shot at Big Ash. A single shot richochets off of a nearby support beam as Bruce Campbell ducks. A shotgun fires a burst of pellets (buckshot), which is no way shape or form would richochet as they are shown to do. Other scenes (such as when Ash shoots off Arthur's sword) are a bit more problematic, even with a sawed-off shotgun like Ash uses. At that distance, even a tight batching of buckshot would probably take off Arthur's head as well.