Well I can't speak to the what you are suggesting but there are two reasons I use it. First my mother's maiden name is McMurray, Murray being a Scottish spelling and Mc being Irish.

The other reason is that there was an article I read sometime ago that talked about the immigrants to the US and the author talked about the fact the becuase both the scotch and irish immigrants were in similar financial situations the ended up living and working together and eventually enter marrying. So alot of the blood got mixed up. Although this wasn't the focus of the article. And no I don't have it anymore unfortunately.