Bob I don't know if this is your guy or not. I did a search of the Gratiot Street Prisoner list in the Civil War in St. Louis site for those men who were captured on July 4, 1863 and got about 16 hits from the total of the three separate lists. This guy fits what you have described

http://www.civilwarstlouis.com/Gratiot/prisonernotes.htm#Abshire