I use paraffin or sawdust. I ran out of the latter a while back and had a bunch of dry oak leaves on the patio. They worked really well.
I spent 8 years working in a solder factory. We'd cast 20-70 lb billets of alloy. A lot of the ideas from that place seem to carry over into bullet casting. What we used to flux the big 600 lbs pots of alloy was chunk charcoal. They used to buy it by the truck load, and I'd buy a few bags off work here and there for BBQ'n. It was great stuff, and really cleaned up the melt in a hurry.
