First, the general idea: What if instead of steampunk, you had
gunpunk? Replaced steam with gunpowder?
Well, let's start with
propulsion. What could replace steam?
-Rockets could be of limited use- one could select a rocket with the appropriate burn time for their journey. I can see this being used for a sort of rail system or flight, such as gliders or blimps. I personally like the idea of a rocket powered Minecart.
-Car Engines work by igniting a bit of gasoline to propel a piston, which in turn propels an axle. Replace gasoline with gunpowder. And back away, as fast as you can. This would be difficult IRL, because while gasoline is a liquid, gunpowder is in granular form.
ClothingThis seemingly 'innocuous' category suddenly becomes important when the world is powered by an explosive!
I'd consider it a given that people living in such a world would quickly learn to wear armour that would probably be ceramic, and similar to RL bullet proof armour. This would make them more durable, and our traditional calibers would be less effective. This will obviously give rise to clunky, oversized weapons for more !!FUN!!. I have pages of ideas for clothing, so I'll stop here.
Architecture Wooden buildings would be a major no-no in populated centres, for the simple reason that it burns. Gunpowder+Fire=A slight problem.
The Orient is well known to have had great metalworkers, especially for their swords. It's not too far a stretch to imagine them extending this to their architecture, although it'd certainly be expensive and quite dangerous. They'd have to have a forge on sight, and I can easily imagine the smithy taking side jobs for adventurers and the like.
In terms of defensive structures, they'd be a tough nut to crack... and a
Hwacha Emplacement would wreck havoc to everyone in its path. Including adventurers. I honestly am cackling at the idea of some fools trying to take one on, more so if you consider the fact that I have a thing which can give me a roll for every single rocket it fires- up to 200 of them, although I will not be that cruel. 50 is probably still overkill. I'd suggest either having inhuman reflexes, heavy armour or something of that nature.