ooopps....see my corrections...it actually the "pin marks" that give away the recent manufacture (IMO).
Yes, investment casting is quite old & casting in general goes back way before with copper-cast tools.
Take a look at an old Colt C&B revolver (inside) to see what I mean...they must have been cast pretty rough, cause they had to grind them smooth enough to fit the grips well (maintaining correct dimensions). I'm guessing confederate manufacture would not be more sophisticated during the conflict years.
Regards,
Slim