doon:
Re CAS shotguns, SIR had some SXS 12 ga. external hammer Norinco 1887 Coach Guns, (Norinco Model 99??)
You can also use any double with internal hammers as long as they don't use ejectors. Extractors only are CAS legal.
You might also consider a Winchester 1897 pump or a clone as they too are CAS legal.
Don't hesitate to show up at any CAS shoot. The cowboys and gals are a great bunch and most are happy to loan a newbie what ever is needed to shoot a stage or two, or three or more.