Found the little cast iron pot tapped out at 15 lbs - very nearly full, so not sure how anyone could get close to 20 lbs, but perhaps they can. I found it really difficult to even get skimming spoon(s) in the pot. There is an issue with one side of the pot having a wall substantially thinner than the other side (looks like it might be overly and unevenly aggressive grinding), but that's a separate thing.
Anyway, wanting to smelt 20 lb to likely 40 maximally at a time. I would imagine things like a 6 quart stockpot, cut propane tank, on that scale, would not be very useful at this scale of smelting - I imagine I'd have a very shallow pool subject to high oxidation due to the surface area. Any suggestions for a container at this level - at least a ballpark volume appropriate for say 30 lbs on avg.?