The small screw on top of the New Englander bbl is the 3rd screw for TCs scope base adapter. Also the 2 screws on the rear sight are used( the screw holes, 3of them). I would replace the nipple and give it a good scrubbing. Use a fuzzy pipe cleaner when the nipple is removed. I clean one end of the nipple w/a pipe cleaner and run a large needle or fine wire through the nipple.