I did some research today at the Missouri State Archives for James CHORN. The only service record they have is for a James Chorn who served in the Mexican War. Are we to assume this is the same man as James M. Chorn?

James Chorn, Col. Doniphans 1st Mounted Reg't, Co. C commanded by Capt. O. P. Moss
Enl: June 7, 1846 at Liberty, MO for 12 mo.
Discharged: honorably on June 21, 1847 at New Orleans, LA

On the back of the service card:
Virginian: farmer
ref: "Doniphan's Expediton Conquest of New Mexico & California" by William E. Connelly

As a relative of James M. (by his wife Nancy Rawlins) I show his birth in Clark County, KY in 1816, as listed in the 1850 and 1860 Howard County censuses. There is no record of him in service to the CSA, but not all records survived so it is not surprising.