I have a Giardinelli harmon-style mute from the good ol' days when they were a real shop on 46th street. This mute had a stupid FOAM RUBBER gasket on the tip instead of cork, though! It seemed cool until about the third or fourth time it popped out of my bell. I ended up putting two strips of sheet cork in the traditional spot, and pushing the rubber back so that it just touched the bell and kept the benefit of a really good seal. That was a pain.