On the barrel lump there is a spring loaded piece that seems to latch to the receiver. What is the purpose of this piece?
I played with few Winchester 21s and had Classic Doubles 201 that has same feature as the one you're referring to. Through manipulation I was able to ascertain that "spring & plunger" helped to keep barrels from opening too wide and seemed to help with closing the action (little less force required). The Winchester model 21 is wonderful shotgun to own and use. Right now you pay premium and get premium back when selling. What the future will bring I do not know.
