IIRC they are pretty much pure lead? Sweet!
Well I certainly would call it "pure" lead, if not elemental lead. This stuff fresh cast tested at 4.1 Bhn, in line with other radiation shielding I've worked with except the 2x4 bricks that I've gotten from time to time. Those run 5.0 to 5.5, which is "soft" by all common definition, but not exactly "pure". This stuff is softer than pipe and roofing that contain a tiny bit of hardening agents to help with the manufacturing process of those forms.
This stuff I call the holy grail of soft pure lead. I snag it up every time I find it, and this batch was got for 50 cents a pound, 324 pounds. I couldn't get it on my truck and gone from there fast enough.
I'm in line to trade into 500 lbs of electric cable sheathing in a couple weeks and that stuff also runs in the low 4's on hardness.