The 8th Mississippi fought in the Western Theater of the Civil War. They were not at Gettysburg, PA.

Here is a link to a unit history that will tell you the battles, in which they fought. I have an ancestor who was a member of the 5th Georgia Infantry, which was a "sister" unit of the 8th Mississippi Infantry in J. K. Jackson's Brigade. I have studied Jackson's brigade and know that ALL of its units were heavily engaged at the battles of Murfreesboro, TN and Chickamauga, GA.

History of the 8th Mississippi Infantry
http://mississippiscv.org/MS_Units/8th_MS_INF.htm

Jim Martin