There once was a small book that had all the history and information of Sheridan air guns...long out of print at one time over $100 if you could find one. Just found out that the original author has now brought out a second edition that is updated with more information. I just ordered one and should be here tomorrow....
https://www.amazon.com/gp/product/1790748615/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
