Thanks for your service! Man there isn't much around there, I would suggest making some phone calls/emails to the Mississippi Department of Wildlife,Fisheries & Parks. Some of the Wildlife Management Areas may have shooting ranges or possibly they can tip you off to a private range in the area. http://www.mdwfp.com/wildlife-hunting/wmas.aspx
Another option is to look just across the state line in Alabama > http://home.hiwaay.net/~stargate/seasons/ranges.htm