Good advice GW. When the lead melts all the jackets, plus sand, dirt and more will float to the top, but it's a royal PITA to dig around the spout column and other features of a furnace when trying to scrape them off.
I can get lead from our indoor range for 10 cents a pound, but I use a small cast iron pot on a Coleman camp stove for the first melt, pouring the good stuff into a gang mold I have for 1 pound ingots, scraping off and discarding all the dross. The ingots work well in furnaces.
As for the lead itself, yeah it is harder than pure lead, though it can be made to shoot in RBs. Recent posts in the Accuracy section of the forums indicate some guys have had pretty good luck with casting alloy conicals too, but not me. They're a booger to seat into the rifling in the first place, and the "minute of backstop" groups I get aren't worth the trouble.