I melted down some Winchester hard #7 shot that I no longer needed to reload 12G. Without having a hardness tester it seems quite hard and the ingots I made have a 'ring' to them rather than a leaden thud. Not very scientific but there it is for what it's worth. From research I did before melting down the lead shot it seems lead shot is around 97% lead and 3% antimony with no tin.

One thing I will say is that the shot lead doesn't seem to cast as well as my usual Lyman #2 mix. I notice it is hard to get consistent filling of the mould and I did read somewhere that it is tin that is needed in a casting mix to achieve good mould fill out.

When making up Lyman #2 alloy I usually use wheelweights, pure lead, and 50/50 lead/tin solder, which in the right proportions gives me a mix of 90% lead, 5% antimony and 5% tin with which I have had great casting success. I intend remixing my shot lead ingots and adding in some 50/50 solder or pure tin if I can get some to try and get a better casting alloy.