Weaponry

Explosives
The telos of black powder is to explode -- a more volatile telos than any other substance in the gameworld. That volatility is conspicuous to a Theurge who’s looking for it, so it’s not easy for someone carrying powder to remain concealed. And it’s very easy for Theurges to accelerate that potential, creating a much bigger and more destructive explosion than you’d get by simply striking a spark to the powder.

So bringing "miner's powder" to any fight involving Theurges would be foolish – a bit like trying to use liquid nitroglycerin in combat. It’s much more likely to kill you than your enemies. (source)

Tunneling
Miners’ powder is indeed used for mining, but not much used in battle, in part because the only war of note for centuries has been carried on in heavily Theurge-ridden areas and across a Ward. Besides not being Ward-crossable, black powder is ungainly (very little tech development has gone into it as a weapon, for reasons explained on the WIP thread) and conspicuous – it’s too hard to keep Theurges from sensing it while it’s in transit to wherever you want it.

Once you’ve got it off a cart or ship and into a tunnel, it wouldn’t need to be all that deep to escape most Theurges’ telos-sense. Twenty feet deep, maybe, to avoid the notice of a sensitive Theurge who was actually walking over it? But Theurgic warfare doesn’t really lend itself to heavily fortified positions anyway; it privileges mobility.

In a civil war/ insurgency scenario, the tactical uses of miners’ powder will somewhat increase, as there will be walls you want to blow up in places that aren’t crawling with Theurges. (source)

Fireworks
Fireworks have not been invented in the gameworld. (source )

Guns
The evolution of firearms on Earth took centuries, starting (in the West) with adapting bell-casting tech to make cannons. In the gameworld, that process of evolution stalled before it had a chance to get started. Just as cannon-making was properly taking off, Karagond Theurgy was developed, and the armies that had started to use crude artillery were literally “hoist by their own petard.” The lesson of those early conquests was that black powder weapons are worse than useless. (source)

In Erezza, some effort has gone into developing ventisputori (wind-spitters), rifles that use compressed air. They can be quite effective against magi at medium distances. This is why the Karagonds have gone to some lengths to confine them to the Halassur front, outlawing them in the rest of the Hegemony.