My take on this is that it's just one of the umpteen gunsmith-peculiar variations of the 9,3x72R.
There were no standards for 9,3x72R cartridge dimensions back in those days (If you have Dixon's books you have seen his write up) and since the 9,3x72R was one of the most often chambered hunting rounds it shows the most variation in chambers. Sometimes I think no two of 'em were ever made the same!
My experience slugging bores of quite a few 9,3x72R barrels is that they tend most often to run much smaller than the oft-quoted .364", mostly being somewhere within a couple of thousandths of .360".
