I would advise you to stick to the same ring size as best you can. If you use a 7C (as I do) for trumpet work then I would suggest using a 7 series mouthpiece for cornet work as well. I use a 7A cup which is a bit deeper than the 7C and gives me a warmer sound than I can achieve with the 7C. Hope this helps, Chris Mayle Principal Cornet, Basingstoke Silver Band --