I was told by a Scottish native that Mac is Scotish and Mc is Irish. Since we know that McCaffery is Irish then the proper spelling is Mc.
We could borrow off the Mickey D's nickname for McDonalds and have Mickey C's instead.
I'm full blooded Scot. 3 of my 4 grandparents were born in Scotland. 2 of those three have a Mc prefix on their name and the other doesn't have a prefix. The one that wasn't born in Scotland does has Mac.
If you must know, the last names are...
McCullough - pronounced McCollock
McKendrick
MacTavish
And yes, my last name is the 4th one that doesn't have a prefix. It's fairly common and is spelled correctly without a P, unlike the English spelling which is more common, but spelled wrong. Damn English.