Here are the pics. There is pressure by the small spring on the back trying to push the shifter to the left barrel. The feeler (front of the shifter) is kept on the right barrel by the hammer. When the right hammer goes forward the feeler is allowed to switch to the left barrel. It works in dry fire. When I switch the selector to the left barrel it wants to double fire. Im not sure what would cause the shifter to move to the right barrel. The whole spring plate moves back and forth with the selector.