Use Pure Lead with Slug Molds

Use Pure Lead with Slug Molds

Make sure you use pure lead for slug molds. Lee dimensionalized the slug mold to take the shrink rate of pure lead into account to arrive at the correct diameter. If you use alloyed lead (like wheel weights), the shrink rate will not be the same and the bullet diameter will be too large. Also, check to make sure the mold is closing all the way. If not lubricated as per the instructions, it will be difficult to close all the way, and this will result in out of round, over sized bullets.