There is a great article that shows a tin type of two brothers(Mays) wearing frock coats one of which was with the 2nd AR Mounted Rifles in Mid 1862 as infantry. As close as you will get to the 1st Mounted Rifles uniform during that period received from the little Rock Prison system. http://www.geocities.com/capitalguards/LRfrock.html

Also, when the first regiments were enlisted at Fort Smith, the 1st Arkansas Mounted Rifles signed a 1 year term. So, when you look over muster records and it lists your ancestor as deserted, check the term of enlistment. Many soldiers drew their pay in June/July 63 and went home if you look at the history of the regiment. As for my ancestor, W.W. Babb, Co F, 1st AR MT Rifles, Left in July 63, year after the term had expired drew his pay, and went back to Cotton Plant. Later in the war, records show him with Dobbins Brigade, taking the oath in june 1865.

Wade W. Babb's brother, Abner, also Co F, stayed with the 1st until captured at Nashville Dec 64 and sent to Camp Douglas for the remainder.

Phillip
Lt Commander
Jefferson Davis Camp 175
Colorado Springs Co