Henh. My take on that is that the shotguns are a colorful feature, but over-romanticized. Some Reb cavalry in the west used shotguns because they could get nothing better. They delivered an effective blast close-up, but had a very limited range. Forrest taught his men to make a virtue of their necessity by charging mounted to close range and then firing a volley. It was a necessity, never a preference. They replaced the shotguns with better long-arms as soon as they could.
If you can confirm that a particular regiment was shotgun armed for a particular battle or campaign, then make a special rule to cover them, but shotties should not be a standard feature of Confederate cavalry.
You'll shoot your eye out, kid!