Hi.
I looked in my books (SCSW#3) and it looks like it can't be a 1903 5th change (last of the 1903's) as they went to 263000.
The next model is called .32 HE 3rd model, and went from 263001-536684 thru 1917-1942. So, it looks like late 30's maybe early 40's?