So, I've had this idea which doesn't fit in my world (I've only got humans), but I thought it was neat so here it is: Dwarves would invent bullpup firearms and here is why.
With early muzzleloading firearms, you have to reach the muzzle of the gun to be able to load it, which poses a problem for dwarves since if your gun is much taller than you it would be difficult to reach. You can't just shorten the gun, since with black powder you need a long barrel to get it to fully burn and give your ball enough power. Furthermore, a long gun would also be unwieldy inside small dwarven corridors, which would be extra important since with dwarves living underground they'd be more likely to be fighting indoors.
The solution to this is to bullpup their muskets. I'm fairly certain that there aren't any significant technological barriers to making it work, there just wasn't much reason to do so in our world. This would let them load their guns normally, without sacrificing power, and make them much easier to carry around and use indoors.
The main issues with this are that having the flashpan so close to the user's face would burn them, and the hearing loss. The flash is dealt with by that plate that sticks out beside the lock, which would hopefully deflect the explosion away from the user. The hearing loss I think could be compensated by the fact that the dwarves, having to fight indoors underground oftern, would probably have much better hearing protection much earlier than in our world.
The immense amount of smoke right in the face is almost as bad as the flash and bang itself.
It's a bit annoying with a regular versions, but with it right there in your face, the irritation to the eyes and nose are prohibitive. And of they make the mistake of breathing, they'd be looking at a minutes long coughing jag.
With them already being underground with poor ventilation, that's a nightmare. If you're out shooting muzzle loaders with friends, and there's no breeze, you can end up with a fairly dense cloud after just a handful of shots. Makes the next round harder to place on target, if nothing else.
But, yeah, there's no technological barrier to hearing protection, so that issue is easy to fix. It's the flash and the smoke. The idea of a partial barrier would reduce the flash to the eyes, but not eliminate it. So you'd want to work in some kind of exhibition of that happening in your story or game. Outdoors, in light, the affect wouldn't be major. But in dim lighting, even modern firearms can have enough flash to screw with night vision.
This kind of weapon in the tunnels that dwarves often call home would be something specialized (imo). They'd have a small number of them either taking the first shot and then fading behind foot soldiers, or firing from behind foot. The smoke lingering is going to be a big problem for the battlefield underground.
Well, I guess you could handwave and say that dark vision isn't occluded by smoke and other particulates. But that assumes you have dark vision in the first place it isn't always a dwarf trait. That still isn't great for the dwarves. Their enemies would end up with an advantage from using those, if you're using d&d style underground races.
Good point, I didn't think about the smoke at all. I don't think dwarves generally have innate breathing protection, so that would be an issue.
I feel like I should clarify that this isn't part of a project of mine, I just had this idea for a generic fantasy world (I guess maybe something Forgotten Realms/ D&D esque) and wanted to put it out there, so I've got no other lore surrounding it about dwarven structures or breathing or darkvision, etc.
That said, I feel like dwarven structures are usually very well lit, so they wouldn't be fighting in dim light much. And I think darkvision seems to be unaffected by bright flashes and stuff- they don't seem to be negatively affected by fireballs or whatnot.