He later enlisted into the 98th Pennsylvania Infantry with many of his former comrades from the 21st Pennsylvania Infantry. He participated in several battles, including the Battle of Williamsburg and the Battle of Fredericksburg. During the Battle of Salem Church, his regiment was forced back to a defensive position in a field, leaving many wounded soldiers behind. Among the injured, McAdams spotted one of his comrades and closest friends, Private Charles Smith. After receiving permission from his commanding officer, McAdams rushed over to Smith's position, placed him on his back, and ran back to his company while under fire. Smith later died from his wounds, which included a gun shot wound to the head. McAdams received a promotion to sergeant for his heroic rescue.