It works quite well in my cornet!
↩ repost
So, I found this design of a 3c Trumpet mouthpiece on Thingiverse, but I have a cornet. I decided to redesign it and make it into a cornet mouthpiece. I just finished printing and it works really well, surprisingly enough.
https://www.tinkercad.com/things/dwymP0ixrpd-3c-cornet-mouthpiece