First off I would soak in warm soapy water for a week. Can't tell how much rust is Built up but try to get the big stuff of the take. Needle nose pliers and crush the rust you can hear the rust snap off I do it all the time to nails with not even soakin them or if you got big iron, soak in water scrub with wire brush and hammer has always worked for me That is the stuff in the middle I have not found enough shells to know what works on them