Considering the commodity price for lead right now is around $1.30 USD, I'd say you're getting an excellent deal floydster. In my area, some people are paying .45 cents a pound for mixed wheel weights. I'm lucky and still have about a dozen tire shops that sell them to me for $40 per 5 gallon bucket. I'm stocking up while I can, and hope to finish what I think is a life time supply within the next two or three years.
As far as the dirt, just heat the heck out of it since you don't have to worry about zinc anyway, but keep it well fluxed. That dirt, sand, and other crap will float to the top where you can skim it off. Consider throwing in a few handfuls of sawdust with the shot, and scrap the sides and bottom of your pot well once it's all melted. Then add some candle wax, and let it ignite (use caution). The reducing atmosphere of the burning wax will return the oxidated metal back into your melt while the sawdust should be converted to a grey light powder containing any impurities. And it makes it super easy to skim off.
Shot makes a good all purpose alloy as is, and it contains a lot of arsenic (more than wheel weights) which makes it harder especially when water quenched. It contains enough tin to ensure proper fill out too, since the machines that make shot employ molds with small channels and proper fill out is important. Even slowly air cooled, your shot will likely have a BHN of 13.
Last edited by Gerry; September 30, 2012 at 04:26 PM.