The civil war post-dates the switch in manufacturing to interchangeable parts with defined tolerances. This makes it a whole lot easier to build and maintain the firearms.
Here in Texas, my grandpa used to participate in these when I was a kid. He would set up a tent in the main camping area and chill out with everyone else partaking. When the event happened they would go act it out, but otherwise it was one big camping day/weekend at a park.
When I was kid in Florida there was enough overlap between Boy Scouts camping and Battle of Olustee reenactment camping that I'd hear stories about the folks involved in the latter. Don't remember much, just that they could never, ever find enough Yankees, and they always made sure they had their battle flags.