BY DAVID DISHNEAU

ASSOCIATED PRESS

SHARPSBURG, Md.

The two privately financed events, both open to the public, were scheduled on back-to-back weekends leading up to Monday's 150th anniversary of the bloodiest day of combat on U.S. soil. About 4,000 uniformed re-enactors participated in last weekend's event near Boonsboro, Md. Another 4,000 plan to take part in this weekend's extravaganza near Sharpsburg, Md.

The dual re-enactments highlight a division between the hobby's so- called progressive wing, with its scrupulous focus on historical accuracy, and mainstream re-enactors more interested in battle tactics and camaraderie than in having the correct number of uniform buttons.

Both groups are dedicated to commemorating the clash that occurred Sept. 17, 1862, on rolling farmland along Antietam Creek, about 60 miles north of Washington. More than 23,000 combatants from the North and South were reported dead, wounded or missing after 12 hours of carnage that began at dawn.

It's unusual for competing groups to mount separate battle re-enactments, but this is no ordinary anniversary. Antietam, known in the South as the Battle of Sharpsburg, is the biggest Civil War event of 2012. Many re-enactors who got into the hobby during the 125th anniversary are now in their 50s, with few opportunities left to join such large battle scenarios. Antietam came nearly 18 months after the war's opening shot at Fort Sumter, and 2 years before the Confederate surrender at Appomattox.

Last weekend's re-enactment was billed as a progressive event, with rules governing everything from the type of shoes worn by soldiers to the number of cannons on the field--just four per side.

"We press the guys to have exact, correct uniforms, as best that they can, to duplicate the appearance so when the public sees it, it's not just generic Civil War--it's like pulling back a window shade looking directly into September '62," said organizer S. Chris Anders of Rear Rank Productions in Hagerstown.

Anders' group has been mounting such events for 12 years. The group's focus on authenticity has won followers such as John Miller of Waynesboro, Pa., whose unit opted for the progressive re-enactment.