...i will try the national archives.
Don't discount that record for Charles McCart that was discharged in 1852.If the only source you have is a marriage cert of the son, the occupation is listed as probably the son told it. I also have marriage certs that list the father as a soldier, but he had been discharged many years previously.Added: Just as a matter of interest...what was the son's name? Are you trying to go back a generation...and all you have is the father on the MC?