13,000 is likely a very liberal estimation, but not far from what is true. Thank you sir!Looking at the SCV's main page, they make the following claim when it comes to numbers:
It has been estimated that over 65,000 Southern blacks were in the Confederate ranks. Over 13,000 of these, “saw the elephant” also known as meeting the enemy in combat. These Black Confederates included both slave and free. The Confederate Congress did not approve blacks to be officially enlisted as soldiers (except as musicians), until late in the war. But in the ranks it was a different story.