Cerrosafe, it's reusable, and can be melted in boiling water, works excellent, see chamber casting in the FAQs. I have a glass measuring cup dedicated to Cerrosafe, I sit in in a pan of water on the stove, while it's "cooking", I use my wife's hairdryer to preheat the barrel, use a patched jag on a rod inserted from the muzzle placed near the throat as a stopper for the casting.
Tim
