Unfortunately, if you go to the following web page: http://www.tngennet.org/civilwar/rosters/cav/cav12/coc3.html it appears that the roster for Company C of the 12th Tennessee (Union) Cavalry, shows Bullock's name as "Ruin T. Bullock." This cavalryman's age is given as "29" when he enlisted in February 1865, which doesn't jive with your ancestor's DOB.