yes we are using the lee 12ga mold that has the key slot in the hollow portion of the slug
Which one? They make two, a 7/8 and a one ounce. It doesn't really matter which one, just curious.
As for the "frosty" look, that's just fine. ALL of mine are a dull silver color, some call it "frosty", I call it perfect!
As for the recommended pure lead, that's IF you're going to be hunting with them. Then you want them soft so they can expand. If made from pure lead, you'll find them a lot harder to make, lots more rejects because of poor fill-out. Also, the need to run the pot as hot as it will go.
To my way of thinking, a 12 ga. hole in the ribs of a deer lets a lot of blood escape, and a lot of air into the lungs, so they collapse. WW lead is soft enough to expand a bit, and is a lot easier to get good slugs with.