Great score....I snagged 500 lbs of lead from my local range and it took me a while to smelt that down. I didn't have but a 25# rig though...I wouldn't do this in more than 75-100# at a time. For one thing...that much hot lead is dangerous if it should accidentally spill. I'd cut a propane tank if I had to do all over again. I wouldn't use ANY water to separate things either. I just let the light stuff float and "dross" it off. The rubber will just burn off and likely you don't have too much rubber in it. Just what came off the backstop in small pieces. If you find larger pieces...pull those out as you go. As stated earlier...just smelt down a few buckets at a time and use them up....store the rest behind the garage or basement for later smelting. Besides...you could use some for bartering too...let someone else do the hard part if you do.
Good luck with it...its gonna take you a while even to do a couple buckets per session.
redhawk