Simply the best-- and I don't say that about much.
Full length buff leather cavalry carbine sling. Originally black, now oxidized to brown, as pretty much all CW buff leather is and probably was within months of issue due to the iron oxide in the dye. Buff leather, 2 7/16 inches wide, 56 inches long-- full length, uncut, not assembled.
Buff leather was used for accoutrements before the war and throughout the war. The key to dating this one is the use of a straight line of stitching to secure the buckle. This line of perforations was eventually found to provide an effective tear line for the belt when subjected to stress- like carrying the weight of a carbine for a long period. The design eventually went to vertical stitching in three lines, or a box stitch, and finally added rivets to the equation just to make sure. This sling dates between the adoption of black belting in place of white in the 1850s and the very early war adoption of the vertical stitching.
Here is a top notch example- no need for excuses.