I haven't seen an original pair of USSS leggings in any public or private collection BUT there is a single tall legging with infantry provenance owned by Don Troiani. I believe this legging is roughly 16 inches tall with four buckles on the side. This does not mean that the USSS leggings were identical but likely similar. I have, however, studied a pair of short leather leggings from the same collection; these were very lightweight, very thin oiled leather, machine-sewn leggings with four buckles on the side. They gave me a good idea of pattern and how the USSS leggings might have been constructed.
There was also a very good mathematical study of original USSS images that I believe Mike Tita conducted (someone correct me if I'm wrong!). He used known constant proportions of the Sharps rifles in the images and calculated the approximate height of leggings being worn in the same photo. If memory serves the height he got was 16 inches. He also carefully looked at the visible tips of some of the straps that were curled towards the front of the leggings; using the same constant measurements he figured that the leggings most likely had approximately SIX buckles/straps up the side.
I know there's a lot of speculation in this area; I've heard everything from seven to twelve buckles and I've actually seen a reproduction pair that had SIXTEEN buckles!!! If you think about such high numbers of buckles/straps and consider period manufacturing techniques, cost of leather/hardware, cost of labor, number of leggings being supplied to the Army, you might start to realize that the people making the leather leggings probably did not want to overburden themselves with up to 32 buckles/straps per pair. Enormous contracts for leather and cloth leggings were let in the winter of 1862-1863; the plan was to issue them to every regiment in the Army of the Potomac....although only tens of thousands were supplied (mostly to the III and V Corps in early 1863), such a high output of leggings in a relatively short time dictated their simple construction and pattern.
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Brian WhiteWambaugh, White, & Companyhttp://www.wwandcompany.com----------------------------------
Randolph Mess, U.S. Sharpshooters