I know he came out of Yazoo Co, MS, so I looked into the other units that formed from that county's citizens, figuring he would have transferred to another Yazoo Co unit. Apparently he transferred into Co K (Yazoo Minute Rifles), of the 10th MS Regiment, which was reorganizing at that time (March 1863) near Corinth. In April 1863, Co K became an unlettered cavalry company known as the Phillips/Richards Co of the 18th MS Cavalry Battalion, aka Chalmers' Battalion, later becoming the 18th Battalion of MS Partisan Rangers.
In 1864, the unit went through several reassignments: Duckworth's Brigade, Rucker's Brigade aka 6th Brigade of Forrest's Cav., McCulloch's Brigade, and ending under Gen. P.B. Starke in 1865.
Locating all of those service records might be a challenge. Wonder who maintained his service records in Chalmers' Battalion, and these various Brigades?
Looks as though this ancestor could have seen action at King's Bridge, Temperance Hall, Walnut Hill, Holly Springs, Coldwater Ford, Collierville, Fort Pillow, Brice's Crossroads, Tupelo, Memphis, and Maplesville. If he stayed for the duration of the war.
His headstone attaches him to the 1st MS Light Artillery, Co B, and that appears to be in total error.