My 20g BSS Sporter had this same problem and found a solution. If I remember right the selector mechanism worked correctly when the right barrel was fired first, but would not switch to the right barrel when the left barrel was fired first. I had the gun many years without noticing the malfunction because I always had the right barrel selected to fire first. My BSS did not have a selector button in back of the trigger, just the shaft with the hole in it, so it was a little difficult to push the shaft to the other side because of the missing button. It was this way when I bought the gun. After cleaning and messing around for a long time, I put a couple small washers on the shaft of the selector and held them on with a little pin through the hole. The slight repositioning of the selector mechanism allowed automatic switching to the second barrel. Hope this helps, Dan
