I have a mystery metal alloy, which I thought was approximately 2/3 tin, based on density. No idea what else is in it, or what it came from. I got it from a pile of scrap lead somebody had melted into frying pan sized ingots.
It gives my ww alloy the right flow properties, like tin should, when mixed for 2% tin content, BUT, my boolits are sometimes showing small pinholes in the bases, even though I pour a very generous sprue puddle. When the puddle frosts over, it looks normal, but when I cut the sprue I find pinholes. No idea how deep the pinholes go or how big the cavities are inside; weight is still within a grain or two and they shoot OK, so it can't be too bad. Anybody know what could be in this alloy causing this shrinkage? These boolits do drop a little smaller from the mold, by almost a full .001", compared to normal WW+2% mix.
Here's a picture of the cooled melt of this "tin" alloy in my 4 lb Lee pot. Notice the large void in the middle? It goes about 1/2 to 2/3 down into the pot. It leaves a void similar to this every time it cools off. I've never seen this before. Tin doesn't do this, does it? I'd like to figure it out, because I've got at least 20 lbs of this stuff.