Yes, this could be a rifle that confederates used. The weapon was one of the best available, and was used by both sides in large numbers.

In my experience, most confederate units used a hodge-podge of weapons, so it would be most difficult to accurately state that a certain Mississippi unit used only this weapon. (I am currently tracking a Sharps carbine that was attributed to a soldier from the Mississippi 19th Infantry; he may have carried it in war, but carbine were almost always issued to cavalry troops).