Mike,
The Model 1 became the Field grade. The S has been argued and fought over for at least 10 years I know of. Bottom line, no one knows what it designates. One discussion (on this board) went 30 pages (IIRC) with no conclusion being reached- every one pretty much decided just to say it meant steel barrels and never bring it up again. Have you discovered those Pa. grouse yet? Should be lotsa rabbits, also. Have fun up there.

Cary