It sounds odd to have a soldier mustered out during the middle of the Gettysburg campaign. On the other hand, a sharp fight involving Semmes' Georgians did occur at Funkstown, Maryland on 10 July, before the army recrossed the Potomac into Virginia. At least two men were reported wounded in this fight from the 10th Georgia, and one was killed, Sgt. Samuel W. Ridley. Ten casualties occurred in the 50th Georgia at the same place. In the 51st, George W. Sellers of Company E was wounded in this fight and lived until 1864; Pvt; P. S. Snuggs of Company B was wounded; Pvt Henry Williams of Company E was wounded; and Cpl Lewis Herring of Company K was captured. So it's entirely possible that Private Charles McCann was killed on 10 July in the fight at Funkstown.