I have made probably hundreds of lead hammers, but they were made of solid lead/ antimony alloy with pipe handles, they are about 2 lbs weight and were made with a mold that an old friend gave me perhaps 40 years ago; one note, although wheel weights are about the ideal hardness for hammers, any harder, and they are liable to spall when struck, (this with hammers made from babbit) resulting in fragments of lead alloy whizzing past our bodies, and every time we remelt the weights/hammers antimony is lost and the hammers get softer and mush over more easily, and antimony should be added to the melt in the form of a lead antimony alloy, what I use for the purpose is 70/30% lead/antimony. One time I made my own alloy when making a babbit alloy, I bought antimony metal and alloyed it partially with wheel weight lead, this can be hazardous to one's health due to the fact that the fume (purple smoke) is toxic, it has to be melted first at red heat, then the lead is added, which I assume also emits fume at that temperature; I did buy a metal fume respirator for the project! Buying the alloy makes more sense. A lot of slag on a lead alloy can be re incorporated by fluxing with powdered rosin, it reduces the oxidised slag back to it's elements, makes lots of smoke, stinks up the place, but works well.