Not much help here, but a Google Search does show that the Blackman family was well established in the Eastern part of South Carolina by the early 1700s. The family story may well be true. My own family tree lists stories of two of my ancestors at the Battle of King's Mountain in South Carolina. However, I have never been able to document this satisfactorily. Part of the problem is that they were irregular "Over-Mountain" men from Tennessee. The same problem may hold for your ancestor. Francis Marion fought primarily as a hit-and-run guerilla, and documentaion for that type of unit is by definition more sparse than for regulars. You can hope to POSSIBLY find information at the National Archives, since Blackman may have applied for back pay or a pension after the Revolution. I wish I could be of more help here.
Santa Fe, NM
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