There were two "Chapman's" batteries from Virginia, both serving at the same time. The Booton-Chapman battery, from Page county, served in the Yorktown peninsula and the fighting near Richmond. It was disbanded on October 4, 1862 due to personnel losses. The battery you are asking about was from Monroe County. Commanded by Captain George B. Chapman, it served in the southwest region of Virginia (later West Virginia). This battery was raised early and continued service in the southwestern Virginia or the Shennadoah Valley region until the first quarter of 1865, then called to Lee's army. As to the "prescribed " artillery uniform, although I have no information concerning clothing specific to this battery, my guess is that they wore a collection of clothing, items of uniform mixed with homespun. This would certainly be true during their years of later service.
Regards
Ron