The S-man name was one that Michael Petrov put on these rifles made by an unknown maker until he could figure out who the maker was. But unfortunately the maker is still unknown. I'm sure the S came from the pistol grip shape. I remember how excited Michael was when I sent him photos of the first one I got as it was something like the 5th one he had seen. He later got the one with the scope shown in the photos that I got from his auction.
Dan