The 31st Ark was transferred from Ector's mostly Texas Bgde to McNair's Ark bgde at the army reorganization in Nov. 1862.
Here are additional timeline details for the 31st:
[From OR's and CSR's unless otherwise noted]
Ector's brigade fought its first major engagement as a unit on August 30, 1862, at Richmond, Kentucky. Colonel T. H. McCray of Arkansas comanded the infantry brigade, attached to Lieutenant (General E. Kirby
Smith's Army of Kentucky.
ECTOR'S BRIGADE IN THE CIVIL WAR by BILLY KURTZ WEST JR., B.S. in Ed. A THESIS IN HISTORY
Officially Mathew Ector received his promotion to brigadier general on August 23, 1862. His rank was confirmed on September 27, 1862; but he did not assume conmand of a brigade until October 31, 1862. This brigade became known as Ector's brigade and consisted of the Tenth, Eleventh, Fourteenth and Thirty-second Texas dismounted cavalry regiments. Colonel McCray's Arkansas Sharpshooters no longer belonged to the brigade… ECTOR'S BRIGADE IN THE CIVIL WAR by BILLY KURTZ WEST JR., B.S. in Ed. A THESIS IN HISTORY
Nov 62 Army reorganization-31st Arkansas transferred to McNair’s Bgde
Organization of troops in the Department of East Tennessee, commanded by Lieut. General E. Kirby Smith, November 20, 1862
Third Brigade Brig. General E. McNAIR.
4th Arkansas, Colonel H. G. Bunn.
30th Arkansas, Colonel C. J. Turnbull.
31st Arkansas, Colonel T. H. McCray.
1st Arkansas Rifles,* Colonel R. W. Harper.
2nd Arkansas Rifles,* Colonel J. A. Williamson.
4th Arkansas Battalion, Major J. A. Ross.
Arkansas Battery, Captain J. T. Humphreys
Soon after the Battle of Murfreesboro, the 4th Arkansas Battalion merged into the 4th Ark regiment and in August, 1863, the 31st Arkansas transferred to the 4th.
http://www.rootsweb.ancestry.com/~armontgo/caddorifles.htm
The Unit History CSR for the 25th Arkansas includes a notation:
The 25th [30th] and 31st Ark regiments were temporarily united in early part of ‘63
2/27/63 Maj McColloch of 4th Ark was relieved by consolidation
Feb. 27, 1863 Martin J. Coughran, Co. H, 4th Arkansas Infantry Reg-Sent to Arkansas as a recruiting officer by order of Gen. Bragg (report dated April 29, 1863, Shelbyville, Tenn.)
In 1863, the remnants of the 4th Ark Battalion Battalion were consolidated with the 4th Arkansas Infantry Regiment
http://www.couchgenweb.com/civilwar/4th_battle.html
February 28, 1863.
Third Brigade.
Colonel R. W. HARPER.
1st Arkansas Mounted Rifles,* Lieutenant Colonel D. H. Reynolds.
2nd Arkansas Mounted Rifles,* Colonel James A. Williamson.
4th Arkansas, Colonel Henry G. Bunn.
25th Arkansas, Colonel Charles J. Turnbull.
31st Arkansas, Colonel T. H. McCray.
4th Arkansas Battalion, Major J. A. Ross.
Arkansas Battery, Captain J. T. Humphreys
Organization of Polk's Army Corps, April 1, 1863.
Third Brigade.
Colonel ROBERT W. HARPER.
1st and 2nd Arkansas Mounted Rifles, dismounted, Colonel D. H. Reynolds.
4th Arkansas Infantry and 4th Arkansas Battalion, Colonel H. G. Bunn.
25th and 31st Arkansas, Colonel T. H. McCray.
Arkansas battery, Captain J. T. Humphreys.
Organization of the Army of the Department of Mississippi and Eastern Louisiana, Lieutenant General William J. Hardee, C. S. Army, commanding, July 30, 1863.
General Joseph E. Johnston commanding the department
FRENCH'S DIVISION. *
Major General S. G. FRENCH.
McNair's Brigade.
Brigadier General E. McNAIR.
1st Arkansas Mounted Rifles, # Colonel R. W. Harper.
2nd Arkansas Mounted Rifles, # Colonel J. A. Willimson.
4th Arkansas, Colonel H. G. Bunn.
25th and 31st Arkansas, Colonel T. H. McCray.
39th North Carolina, Colonel D. Coleman.
Depleted by deaths and desertions, the 31st Arkansas Regiment and the 4th Arkansas Battalion were consolidated with the 4th Arkansas Regiment on September 1, 1863. With barely enough men left to fill up two companies in the consolidated regiment, the 31st Arkansas boys served under the 4th Arkansas Regiment’s Colonel Henry Gaston Bunn until the end of the war.
http://www.couchgenweb.com/civilwar/31stindx.html
31st Ark consolidated into 2 Co’s
4th Ark Bn consolidated had already been consolidated from 4 Co’s to 2 Co’s
4th Ark consolidated 6 Co’s into 2 Co’s
9/19/63 The 4th/4th Bn/31st Ark consolidated went into the Chickamauga battle with an aggregate of 250.