Re: Cavalry shotguns
I'd like to add a thougth here. When shotguns are used in the hobby, it seems almost universal with reeactors to use the sawed off or coach gun models. I know there is the example of the extreme short version in EoG, but I'm not sure I buy into the "they were all sawed off" theory. I'm more inclined to think that shotguns were probably left with long barrels. I think this may have been the norm simply because of the manner in which cavalry commanders (at least here in the west), were deploying their troops. As Mike mentioned, cavalry was being used largely as mounted Infantry. Maximum firepower on the ground would have been the preferred effect. Shotguns, because of their smoothbore definition, are not overly effective anyway. However, when you saw the barrel off to the point that you have a hand howitzer, I'd argue that your effectiveness would have been even more weakened. The longer the barrel, the better your range with certain types of ammunition.
So, if you are going to get a shotgun for early or even mid-war scenarios, I'd go with a regular length barrel and avoid the coach guns you see at places like Dixie. You can run across some good shotgun deals at gunbroker.com from time to time.