What does Zinc do in bullet metal? Does anyone have any experience with Zinc?

Fortunately I have never experienced zinc in bullet metal. Those who have report that zinc in a pot of lead alloy will ruin the whole pot, creating a mixture that will have the consistency of lumpy oatmeal and incapable of casting well filled-out bullets. The good news is that zinc contamination is often talked about but seldom occurs. Many of the newer coated wheelweights are feared to be zinc, but seldom are. In most cases the coating will float to the top and be skimmed off when fluxing. Because zinc DOES exsist, it is best to clean and flux wheelweights in small lots so as to not contaminate all your metal at once. In more than thirty years of casting I have seen exactly three steel weights. Steel weights are easy to deal with, they will never melt, will stick to a magnet, and will be found on top of your pot. I have also found five weights that are a flat shape, held on by a separate clip, and look like gray plastic. These will be marked in grams (10, 15, 25, etc.) and will neither melt nor stick to a magnet. They also float to the top. I have no idea what they may be. That is the sum total of weights that did not make good bullets, out of many hundred pounds of wheelweights. Hope this helps, curmudgeon

I once bought a large quantity of bullet metal from a now defunct gun shop in Reno Nevada. It waas supposed to be 1 in 10 tin and lead and was harder'n hell. Stuff wouldn't cast for beans. I later determined that the metal was contaminated with zinc. here this stuff sat for about 20 years with me trying to figure out what to do with it. I didn't want to gyp anybody by selling it, not even a scrap metals yard. I'd read someplace where a guy literally cooked his metal for several hours, skimming off the crap that slowly worked it's way to the top. Well, using a Coleman stove and an old dutch oven, I cooked that stuff and skimmed for three different days before whatever the contamination was finally stopped coming up. Now, with very frequent fluxing, that metal casts a decent bullet most of the time, and when heat treated and water quenched makes the hardest damned bullets I've ever seen.
Prior to cleaning the metal, I figured it was either aluminum or zinc contaminating the melt. Based on the weight of what I removed, I'd have to go with zinc. Yes, zinc contamination does happen, but you can sometimes salvage the metal for some use.
Paul B.