We're (Taylor and I) currently using lead sheeting from an X-ray room wall. It's very thin, but we've a fair stack of it. I have to add 1/4" of 50/50 bar solder to a pot of 20 pounds to make it castable without excessive drossing and colouring. I've not had that trouble with lead before - perhaps this stuff is similar to that 99.97% pure stuff. It is wonderfully soft.
Robert, we're not suggesting you have to alloy for round balls, just that in some guns you can use the harder alloys which are much easier to find, especially WWeights. Too- in some rifles, you can use WW alloys for hunting, which improves penetration on dangerous game - yes, we know deer and black bear don't require hardened lead - but, if your gun shoots it, so much the better.