Cowboy Action Shooting
Cowboy Action Shooting (CAS), also known as Western Action Shooting or Single Action Shooting, is a competitive shooting sport that originated in California, USA, in the early 1980s. Cowboy Action Shooting is now practiced in many places with several sanctioning organizations including the Single Action Shooting Society (SASS)
CAS requires competitors to use firearms typical of the mid-to-late 19th century: single action revolvers, lever action rifles chambered in pistol calibers, and side-by-side double barrel shotguns (also referred to as a Coach Gun – with or without external hammers, although automatic ejectors are not allowed) or 1897-style pump-action shotguns with external hammers. Winchester 1887 lever-action shotguns and Colt Lightning pump-action rifles are also legal. Both original and reproduction guns are equally acceptable. All CAS handguns must be "single-action", meaning that the hammer must be manually cocked before each shot can be fired
(taken from Click Here)