Hello. New member, first post. I recently acquired a MS420. It has been rode hard and put up wet, but I like it. With the help of members here, I am hoping for answers to a couple of questions. I have spent hours on line, can't find a copy of Jon Speeds book, without answers to the two questions: What year was it manufactured and why does it have a third swing swivel on the barrel like the MS 410? All parts have matching serial numbers, including the receiver, barrel and the stock. Proof stamps are the trio of B, U and G. Many thanks in advance, Al