Okay, twelve hours with no attempts, so here's the answer:
It's the lead. All precious metals (silver, platinum, gold, etc.) are weighed in Troy ounces while other materials, such as
lead, are weighed in standard (Avoirdupois) ounces. A troy pound is 12 troy ounces, and each troy ounce is 480 grains,
making a total of 5760 grains to the pound of gold. A standard pound is made up of 16 ounces, where each ounce is
437.5 grains, making a total of 7000 grains to the pound.
So, a pound of lead is heavier than a pound of gold, even though an ounce of gold is heavier than an ounce of lead.