I have a break open single shot Model 220 - it has an interchangeable 20" 20ga barrel and a 30" 12 ga barrel. There is no serial number, but a stamped "Z" (symbol) with an "I O". The 12 ga barrel also has an "A" whereas the 20 ga barrel only has a small "20" stamp. Can anybody help with the history and vintage of this gun? Thank you, ojs5.