Donna, the site Civil War Soldiers and Sailors System sponsored by the National Park Service lists Benjamin F. Buck, George W. Buck and James M. Buck, all privates, as being in Co. A, 49th Tennessee Infantry Regiment. Co. A was from Montgomery County, Tn. The book "Tennesseeans in the Civil War, Part 2" also lists these men in Co. A, 49th Infantry Regiment.
Below are the web addresses for the Civil War Soldiers and Sailors System and Tennesseeans in the Civil War.

http://www.itd.nps.gov/cwss/soldiers.htm
http://www.tngenweb.org/civilwar/csainf/csa49.html

Do you know if these men lived in Montgomery County Tn. before the war in 1860 and if so what part of the county they lived in?
A census look up as to where these men lived before the war might further confirm your relatives being in the 49th Tennessee. Hope this helps.