I worked at a circuit board factory for a number of years, and left with 100 or more pounds of scrap 60/40 tin/lead solder. I cast them up about a pound at a time, to add to other alloys, so they'll completely fill out the molds. They each weigh about 180 gr. when I use a a 230 LRN mold, and tirating the amount of tin needed is pretty easy.