It sounds like you may have the same shotgun I have. I did some digging on it when I was working on it (the gun had been frozen for about 2 years) and came up with the following:
1. The gun was manufactured for the public from approximately 1960 to 1972
2. New, it sold for approximately $96 and currently is worth approximately $250
3. There is no manual for taking it apart and reassembling it (it took me 4 days to take it apart, clean it up, and get it working again)
4. Beretta does not carry replacement parts for it, and, in fact, does not even like to admit to having made it (it took me close to 15 minutes on the phone to get them to admit to having manufactured it, after offering to give the customer service rep the serial number)
5. The model name for it, through Beretta, is officially the Silver Pigeon SL 2
Hope this helps. If you have any other questions, feel free to email me:
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and I'd be happy to discuss the gun with you further.