Hi, my two cents of oral history for what its worth...in our family it was the reverse of yours...my paternal grandmother, a MACKinnon, changed the spelling of her name on all records to MCKinnon so as to not be mistaken for a Catholic. This was in Nova Scotia in the early 20th Century and her family were all adamant Presbyterians, later United. Clearly spellings are to be taken with a little salt, but the story handed down in our clan suggests MAC represented the Catholic version and MC the Protestant. Still, the original emigrants to Canada were Protestant but spelled it with MAC on a few records...so whose to know for certain...? Same story, but obviously with regional differences that will vary between families and geography. FYI folks. Anne