The Mexicans had worked out a set of regulations for conducting Mexican Silhouette competition to achieve uniformity of conditions in their various range locations. The size of the silhouettes types and size of stands, range distances, shooting equipment allowed and match operation procedures, were all spelled out before any match was shot in the USA. When Silhouette shooting started in the USA, the Mexican rules were adopted with very few changes. Probably the most significant change was to add horns to the sheep target to give it the appearance of a Rocky Mountain Sheep. The rules used in Ireland are those of the National Rifle Association of America (NRA). The official NRA rules were adopted in Ireland in May 1992. The National Silhouette Association of Ireland was formed in July 1994.