The 5th Regiment was captured en masse at the fall of Vicksburg on July 4, 1863, and McCown was taken prisoner. He was exchanged and assumed command of a regiment consolidated from the remnants and exchanged prisoners from 5th Regiment, and the 3rd Infantry Regiment. McCown led this consolidated regiment, now part of John Bell Hood's army, in the Atlanta Campaign and the Franklin–Nashville Campaign, where it fought at the Battle of Allatoona.