I am loading lyman 525gr slugs. I bought em from http://gardnerscache.com/12_gauge_sabot_slugs.html

The guy is a little flakey and rips you will shipping, but I never cast bullets.

So far, I have only tried Unique, but have some with WSF loaded. Ok results of 3" groups at 50 yards. But I expect better.

You have to have a fold crimper.

I also am working up some loads from BPI http://www.ballisticproducts.com/
for bluforce slugs with roll crimper.

I suggest you buy a lymans shot loading manual. Last section has loads for slugs. Also buy the BPI slug loading manual. You can actually get by without a MEC shot loader or simular with the BPI and roll crimper.