I melt tons of lead each year and use all sorts of lead,the worst for exploding is used fishing weights ,moisture and ecpecially salt crystals get trapped in cracks and inbetween the eye and the lead ,as mentioned earlier the best way to prevent an explosion is to introduce the lead first into the pot as you begin to heat the pot up or as in my operation i use a tiger torch to evaporate any moisture before putting it directly into melted lead,hope you guys are wearing masks with the proper filters ,lead is at its most toxic state as it cools(vapours coming off it)just something to keep in mind.