I too used an standard RCBS cast iron pot - I used it on a two burner Coleman camp stove with the wind screens up and only the larger burner. Found it seems to make a difference to keep some liquid melt in the pot when adding more wheelweights - seemed to melt faster. And definitely be prepared for a steam/melted lead spray if even a drop of moisture on a wheel weight - inside the clip I think they hide. Hurts like a bugger to pick that off your lip, forehead, where-ever... Would think much less chance of that melting down lead shot, so long as it was kept dry.
As well, I like "cheap" so I use sawdust from my crosscut miter saw as flux - fir, spruce, whatever got cut the last time - seems like you want the organic - sawdust, bees wax, etc. to get mixed into the melt and the carbon seems to float all kinds of crap out - I use a paint stir stick size splinter from spruce firewood as my stiring /inside of pot walls scraping stick - it gets charred up, too, but cheap, and I like "cheap".