Lead is a component used to make all types of conventional ammunition except for 12 gauge coin shot, which requires Legion Denarius instead. Lead may be obtained by disassembling ammunition or converting scrap metal at a reloading bench, with different rounds yielding differing amounts of lead; one piece of scrap metal yields 200 lead.
Both the image and the in-game model used for lead look exactly like the ones used for scrap metal.
Even though lead has its weight stat showing "0.00", it is simply a weight that falls in the thousandths (items that are actually weightless have a weight display of "--"). Each piece of lead has a weight of about 0.0013999904. To put it in perspective, every 714.5 units of lead is equal to a full unit of encumbrance. It's trivial to obtain tens of thousands of units, making the total weight non-trivial, and have no idea of the source of that portion of your character's encumbrance unless you are aware of this "hidden" weight. A later update changed the weight value to display the aggregate total, not the individual amount, making it much easier to see the total weight of your lead supply.
