Dennis.... hahaha, yep SC maker from the Lexington/Batesburg Leesville area west of Columbia towards August GA. Quite a family, I do think this one was always percussion. The side plate certainly looks to be a stabilization effort, and the breech is definitely a hand made attempt to keep the gun in working order. I'm wondering if at some point it blew up in that area. I have lost my pictures of the two rifles on display at the Lexington county museum. I think the trigger guard is a pretty good match, the cheek rest, and the two piece butt plate look to be close but the stock architecture doesn't look right and it has a mix of pins and keys to hold the barrel in place which isn't right either according to my notes but that could just mean its been restocked or the barrel was shortened and reworked. I was hoping someone might come along and have some info to help justify what I think is right or remind me I'm way off base. Dennis, hope you are well and Happy Thanksgiving.
Matt