One of my cousins is named Matthew. He was called Matt in school. When he got his first job, there were four other Matts, & several others that share his surname. His middle name is so common that he could not use it. So, on his first day, his boss told him, that his name was now Mack. Thirty three years later, we all call him Mack. IDK if he is called Matt by anyone. Even his Mama & Papa call him Mack.
I have a friend that is named Maximillion (spelling?). He is called either Max, or Mack.
The “nick to” in the subject line is a nonce usage – it might be understood with context in conversational American English, but it is not an established term.
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Regarding the OP, former MASH* actor McLean Stevenson comes to mind.
The given name “Macklin” or “Maclin” is out there in the wild, but is not common.
Muddy Waters’ real name was McKinley Morganfield. If he wasn’t given the nickname Muddy by his grandmother he probably would have been called Mack Morganfield.