I managed to get a better picture of the barrel shank, it looks like part of a symbol (a wing) can be made out.
Also, what do you mean a casting? I had a gunsmith supoosedly check the headspacing but given I can't even be sure what it's chambered in I'm not so sure now
It doesn't appear to have an S on it, only a K. But it's very difficult because no clearly visible markings are available (I think I can make out a single digit but can't tell if it's a 1, 7, or a deviously shaped pit/dent).
It also has no barrel bands, and the rear sights appear to be not...