bunn

I presume 'pig-lead' is pigs (i.e. small blocks) of lead, in the same way pig-iron is small blocks of iron. (The origin of the phrase being that the square moulds are laid in parallel lines, with a feed trough from the smelter down the middle, and runnels to each mould. The overall effect being of piglets feeding at the trough or, if you have a lot of imagination, from their mother.)