" I did find a desirous record for John Martin and it said he was born in Ireland and was in
Company C 8th...............and was captured on July 4, 1863. But ended there."

Where did you find this record?

I ran through the Casualty analysis for all the regiments, 8th, no joy. Again, no telling how complete these records are. Could be a missing digit, i.e., 38th, etc.