What bits for keyholing cymbals (tempered copper based alloy)?

I have several cymbals with slight cracks in them and I want to keyhole them to make them last longer. What drill bits should I use? I know you should surround the crack with duct tape and don't drill quickly so you don't untemper the metal. We have DeWalt Pilot Point Tip bits ranging from 1/16 to 3/8.