Authorities say Roger Grate shot Darrell Doctor in the head on Dec. 25, 2016, as family members gathered for the holiday at Grate's home in Loris.
Prosecutors said in a statement that Grate and his stepson were arguing when Doctor tried to stop the dispute. Investigators say Grate told Doctor to leave, then shot as his nephew walked toward him.
Grate's lawyer argued that he acted in self-defense.
Prosecutors say a Horry County jury deliberated two hours Thursday before finding Grate guilty of murder.
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