system
Given the following post, respond as if you're commenting on Reddit:
human
[LotR] There's this odd grey dust that comes up from time to time. It's flammable, it's explosive, it's destructive. As I've heard, it's already used in fireworks and taking down fortifications. Why don't we try to make compact weapons out of it?

Say, a machine that could use the combustion to fire deadly balls of steel for leagues? It could take down those pesky castles and armies from quite a long distance.
gpt
It's a problem of metallurgy. Short of Mithril, which is extremely scarce and no longer being manufactured, finding metal of suitable strength to produce cannons that will not crack or explode when fired is a difficult proposition.

Additionally the secret of its manufacture is known only to two of the Istari, one of whom met his end at the tip of his servant's knife and the other of whom retreated to the West not too long ago.