From May until September, 1864, Army's of the Cumberland, Ohio, and Tennessee combined expended 22,137,132 small arms and 149,670 artillery rounds. [at a force of Confederates that barely amounted to about 64,000 men (D. U.)] . On the other hand, the Army of Potomac, for the months of May to Nov. 1864, lost nearly 1/3 of its force to combat casualties (about 64,000 men).
I believe the Confederates were getting more band for the buck than the Unionist.
Soure: The United States army and navy journal and gazette of the regular ..., Volume 3, 1865-66.