I too, have used many things to flux the lead pot with, but the best that I have found and used for 16 years now is GAR Flux. It is designed specifically for bullet casting. Contons no chemicles, paraffin or petroleum. It does not catch fire or STINK. Matter of fact, it smells rather pleasant. That is, compared to most other flux stuff I've used.
Call GAR to order at 973-754-1114 for $5 for an 8 ounce jar. It lasts for a very long time since you only use a small amount. I have a new back up jar.
He sells them 3 for $12.50.
If you haven't heard of GAR before, call and ask for a catalog. I bought molds and stuff from them 16 to 18 years ago. The kid is now running the joint. Their prices are better than most any place. Anything you need pertaining to casting, they most likely have it.
Their Saeco 4 cavity molds sell for $87 each. Midway, MidSouth and the others want $109 for the same mold.
The address is 590 McBride Avenue,
West Paterson, NJ 07424
Email: garreloading@aol.com