To quote from Steven Mullinax book Confederate Belt Buckles & Plates page 182 "Unique style made locally for an independent company from Warren County, Mississippi, known as the Vicksburg Sharpshooters. The Sharpshooters organized in 1860 and muster into Confederate service during May 1861 as Company E of the 12th Mississippi Regt". Arriving in Manassa Virginia by train on July 22,1861. As you stated they could have been made for other Confederate unit, but none with the name Vicksburg Sharpshooters in the Virgina theather, so it seem that this company had them specially made for them since they were formed as a unit in late 1859 or early 1860 in response to the John Brown raid on Harper's Ferry, Virginia, in October 1859.