About 700 people watched as about 600 re-enactors fired blanks from their muskets and cannon.
Gun smoke hung in the air as volley after volley fired with no one falling.
Union re-enactor Ron Yoder, 43, of Lancaster, Pa., had said earlier that "casualties" start to occur when the soldiers run out of ammunition or when they get tired.
"Sometimes they tell you when you are wounded," Yoder said.
Event coordinator Ronnie Paull said he was pleased by the turnout for the re-enactment.
"We couldn't have asked for more beautiful weather," Paull said.
Just like the Battle of South Mountain is overshadowed by the more famous Antietam battle, Saturday's re-enactment has been overshadowed by the "super big, mega event" of September's Antietam re-enactment.
The Antietam re-enactment is expected to draw more than 10,000 reenactors and 50,000 spectators on Sept. 12-14.
Paull said he would like more people to know about the importance of South Mountain.
The proceeds from the event go to the Central Maryland Heritage League, a volunteer organization dedicated to preserving the South Mountain battlefield and other sites.
Phyllis Keller, 56, of Inwood, W.Va., watched the 40-minute battle from the sidelines.
"My poor son got killed again," she said after watching her son fall in the battle.
She could spot him among the uniformed ranks because he's tall.
"They didn't know how to duck," Keller said. "They just stood out there and fired at each other."
Saturday's reenactment covered the action at Fox's Gap. The reenactment continues at 1:30 p.m. today recreating the action at Turner's Gap.
The Battle of South Mountain was fought on Sept. 14, 1862, after Union soldiers found a copy of Confederate General Robert E. Lee's invasion plans. Federal troops fought the Rebel forces at three South Mountain gaps, forcing Lee's troops to retreat to Sharpsburg where the Antietam battle was fought three days later.
The encampment is open from 10 a.m. to 3 p.m. and admission is $10 per car. The proceeds go to the Central Maryland Heritage League.