Two details do not look correct for an original horn. First, most horns with screw-out noses are funneled behind the removable nose, creating a shallow funnel for loading powder more easily. This horn appears to be flat behind the screw-of nose, suggesting it is a modern interpretation. Most original horns or the Civil War era used iron pins to attach the butt plug. Use of small brass brads with raised heads is almost always a modern detail.
Shelby Gallien