I think the first major application for a steam engine that could do real work was way into the 18th century or something, with the steam pump, to access coal seams deeper in the ground by pumping water out. Not sure entirely though.

Hero (a dude) of Alexandria made some steam powered stuff around the dawn of the 1st millenia, and some roman dude put steam powered doors in his house, I think some temples had steam powered doors to.

The emporer, I think Augustus the first one, had it presented to him to develop it further and he decided he didn’t want to take jobs from the plebs or whatever, had to keep the beggars busy with something. So they dropped it.

Hundreds of years prior, a couple of hundred maybe, Archimedes theorized a steam cannon.

Lead is denser, it weighs more per volume, so it travels farther and faster when propelled by an explosion. Uranium works even better, which is why they use depleted uranium in some military applications, as it’s more dense than lead, quite a bit better. Gold or platinum would work better too as they are heavier.

Fun fact, in a half billion years or so, the element of uranium decays into lead.