Re: Old 12 ga. Hammer Gun
The only "Bay State" shotgun maker that I have listed was considerably before the time period you mention.
"Bay State Arms Company - Shotgun maker in Uxbridge and Worcester, Massachusetts, c.1873-74."
But, what I think you have is the Model 7 or 9 Bay State which was a model of Harrington & Richardson shotgun made from 1908 until 1942.
This was a utility-grade shotgun, and doesn't have any collector interest. According to the Blue Book, it's value is:
98% - $95
95% - $70
90% - $60
80% - $45