Unless you have a big supply of lead and a continuous supply, I wouldn't mess with it. The law has changed (2008)to outlaw lead wheel weights and most States started earlier. It's hard to find wheel weights without Zinc in them and they don't run in the shotmakers. I started in 1987 when the tire shops would give you wheel weights just to be rid of them. Not the case anymore.
I suggest you hit the search and find more information on shotmaking.
I actually emailed James Stewart, the maker of the "Better Shot Maker" about using what kind of lead.
Below is his response
"Car Wheel Weights are the best; no stick on weights or trucks weights-these have alot of babbit in them that will clog the drippers.
If unable to get a good supply of car weights you can mix soft lead (plumbers lead, x-ray lead, etc) in with the car weights (70% car weights to 30% soft lead) if making #7 1/2 shot. All other sizes are smaller than the 7 1/2's.
If you want to make #9's you have to use 100% car wheel weights in my machine or your drippers will clog shut.
Some people are purchasing Antimony and Tin and using all soft lead but I do not know the amount of these items to put in the lead. I am not a chemist.
I found this to be interesting after ohters said the same thing as above about wheel weights.