Charlie, with a name like that you have a tough row to hoe. Go to this site and put in James Smith and Mississippi and you will find 35 James Smiths listed, any one of whom could have the middle initial B. You will also find 6 that definitely do have B for a middle initial. There you have 41 possibles. By only putting in the first initial J, the number of possibles increases even more.

http://www.itd.nps.gov/cwss/soldiers.cfm

After you have pulled those lists up, go to the following site and page down to Rankin County and you will see all of the possiblities if he joined a unit from his county (and you can only hope that is the case). At any rate, using this system you can eliminate many of them, and narrow your search a bit. Good Luck

http://humphreys1625.homestead.com/UnitIndex.html