We got a little side-tracked talking about Ferguson's Brigade (although it was an interesting side issue and Alan Pitts provided some good information). I referenced the writings of a Lt Col Frank Montgomery, of the 1st Mississippi Cav. Looking back, his memoirs are avaialable on the internet, through the University of North Carolina at Chapel Hill, at:
The 1st Mississippi was also in Armstong's Brigade in the Atlanta campaign, so Montgomery's memoirs could be helpful. At the bottom of page 190, Montgomery begins to talk about the action of July 28th.
Is the 2nd Mississippi the "4th Mississippi" that fought at Thompsonís Station on March 5, 1863? If so, Armstrong was also its brigade commander at that time. My ggg grandfather's unit (17th Tenn Cav Batt aka Sanders' Batt) was also in that brigade in that action.