As noted, no real work has been done on west Tennessee federals. partly because there were so few. Other than USCT, it pretty much limited to the 7th TN Cav(US), Bradfords battalion, and Co.G of the 10th Tenn Inf and part of Co.A of the 11th.
For some details on Bradford's look for a book called "River Run Red". It discusses in detail the events around the Ft. Pillow massacre of 1864. Bradford's made up half of the Federal garrison. I would assume your ancestor was probably there.