I have a Springfield "Humpback" 12 g... The only markings on this gun is--- Springfield-- Automatic-- shotgun. Springfield Arms..Utica NY. USA. That is it.. No model number...no proof test stamp.. NOTHING!!! It has a low 23xx serial.. What do I have (model) and how old is it??? I would guess 40's, but maybe older.???. Most of the receiver pins are the older screw type pins..Very heavy duty.. thanks for any info..