Jack, The 4's toward the front of your bbl flats, left side of your picture, are the chokes, Full/Full. The 4 at the rear of your bbl flats is the grade. The only marking on the bbl flats of mine is the ser no, and appears to be the only mark that was ever there. Mine also has the "Nitro Powder Approved" stamp on the lug, and like your's it's only about 3/4 there. Don't really know why mine doesn't have the chokes and grade stamped on the flats, it does have the grade on the fore-end iron.
Curtis
