I think this guy is the son of James Smith and Mary Johnston (the middle name is a big give away) Here is his baptism record. "Scotland Births and Baptisms, 1564-1950," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:XY8Y-6PJ : 10 February 2018), John Smith, 08 Feb 1831; citing , reference , index based upon data collected by the Genealogical Society of Utah, Salt Lake City; FHL microfilm 1,041,005. Also the people I'm working with are mostly from Campbeltown.
Birthdate says 18 Feb 1831 His gravestone pretty clearly says Aug 13 1833 I know grave stones aren't always accurate. I can't find any other baptismal records with that date.
I also found a census with James Smith and Mary Johnston with a John born 1834. In Campbeltown. Should I go with that instead of the date on Grave?