What a load of faff. why on earth do you need to 'pre warm' the lead? eat a couple of tins of beans. put cleaned tin on primus stove, cut lead up to fit in tin, put into tin one at a time waiting until the first one melts. Throw some tallow in. That will clear it. pour slowly into a very dry mould. wait for it to cool, then knock out. easy. I do it in a field.This weekend I was involved in lead fishing weights being cast.
The heat was from a Primus stove. The cruicble was a SS steel pot.
The lead was cut into strips and pre warmed on a 1" steel plate on another stove.
The crucible was warmed and small amount of lead was added untill a pool was formed.
The warm strips were fed in and allowed to melt in their own weight.
When there was jst over a pound of liquid lead, the cruicible was poured into a pouring flask. Yes another stove. The dross was cleaned off.
The lead then was then decanted into moulds.
Simple and fun.