Your chilled shot should contain antimony and will not be soft lead. Like stated, sell it to a shotgun reloader.
Like cadman stated, I use all kinds of lead. I have plummers lead, lead from radioactive medicine containers, lead from X-ray rooms, printer's lead and wheel weights. I have had a few molds that were a bit finicky about pouring but on cadman's advice I bought some Frankfort Arsenal drop out mold release spray and cured their problem.
I'd latch onto that $1/pound lead before the guy changes his mind.