John,
The full history of H&R shotguns of all types and models can be found in "THE BLUE BOOK OF GUN VALUES" by Steve Fjestad in any of the editions from the 29th, up to the 33rd which will hit the shelves in April 2012. Listed in the H&R Arms Inc. section - they are layed out model by model, years of production, major features, etc and a short history of the single barrel guns. It is currently the "best" compilations of H&R shotguns. Note older editions can usually be found at gun shows and usually sell for $10, rather than 40 - 50 bucks for the newer or current edition. Good luck. The info is far to complicated and long to type out on this thread.