I recently acquired a Stevens 311A SXS with the right barrel being a 410 gauge shotgun and the right barrel being a 25-20 rifle barrel. I have scoured the Internet looking for information on this model but have found no reference. There is no serial number but it does have the marking under the hinge and marking on the watertable. I have seen the sites instructing how to interpret these markings but have not researched the manufacture date. The Monte Carlo walnut stock and fore end are highly grained. Do I have a custom built gun or was this a standard production model?