The gun in question is 6 lbs 7.2 oz. Left barrels wall minimum is .045 and right barrel .043. I suppose if I wanted a 6 lb gun the walls might end up in the low .020's.

I haven't had anyone address the numbers/letters on the barrels that are not the serial number. I wonder if this was some type of cataloguing system Ithaca had.

Nothing is foolproof to a sufficiently talented fool.