Well it looks like SD is catching up to the times. The GFP dept is having a meeting next month to propose rule changes for muzzleloader hunting. Peep sights, 1x scopes and smokeless powder and Blackhorn would be all legal if the proposal passes and would take effect after 20 days . Right now peep sights, scopes and smokeless are all illegal.
Only open sights , even Blackhorn isn't legal.