hmb, I can think of one very good reason, theft. If you are a member of a co-operative club and they don't care that's fine. One of the local clubs I shoot at is privately owned. I know the owner, he estimates there is a million pounds out there, and that shot is his.
Having retired from Delco Remy / Delphi. Don't waste your time with battery lead, I had a chance to buy 4 tons of the stuff. Tried it in a littleton shotmaker & it plugged the orifices up. I took a sample to the engineering lab, and was told that battery lead contained SALT & ALUMINUM. Plus you will have sulphuric acid to contend with as a vapor when heated.
Jethro1629 is correct about battery lead. It doesn't make good shot and will gumb up your oriffices on your shotmaker. The best lead for making shot is car Wheel Weights. Jim Stewart has been making his own shot for a long time. Send me an email address and I will send you pictures of the Better Shotmaker and his set-up. You can also visit the web site at:http://www.geocities.com/jstewart1934/My_page.html