Looks to be a Saur built between 1880-1890 as what ever called their Field grade. The date guess is based upon the lack of proof marks and country of origion stamps. The forend iron shows what could be a "Lindner bump" but I doubt it because of the lack of adornment. Might want to remove the forend and check the bottom of the barrels for two crossed pistols which would indicate manufacture by Lindner but I wouln't hold out much hope. The condition appears to be well worn but have it checked out by an expert. May well be the best duck gun you will ever have shot (with appropriate ammunition).