Investigators say the Ohio Fire, which burned more than 2,000 acres northeast of Hailey and forced evacuations, was started by an ammunition spark at a backcountry shooting area.The Blaine County Sheriffs Office released new details Wednesday, saying six people were shooting firearms on Bureau of Land Management land across from the Hurtig Shooting Center in Ohio Gulch when the fire ignited on July 18.Sheriff Morgan Ballis said the area is known…