Recently I did a little Twitter thread on D&D weapons technology spurred by someone elses. Let’s summarize and expand! The question was simply “firearms in D&D yes or no” and expanded to “how to model”. The most popular was of course tinkering with hit and damage and crit and advantage and so on because those are the tools you have. These tools are not sufficient to deal with adjacent technologies because the interesting difference between adjacent weapon technologies isn’t usually the damage they do since that’s not really militarily significant (and weapons technology is about military use not duelling).
And choosing a weapon in D&D is about duelling and not military factors (this will be important later). The difference is more often ease of use, reduced recurring cost, and side effects. So bow to crossbow: the difference is that you need less training to hit something. That’s pretty much it. Crossbows are great if you have a bunch of peasants and no time to make them archery experts — relatively flat trajectory and, most importantly, you point it and pull the lever. There’s just not that much technique involved.
The difference between bow/crossbow and early black powder firearms is: even less training (flatter trajectory, eventually), reduced recurring cost (casting bullets is way cheaper than making arrows), and noise (morale side effect). That is, militarily you pick a black powder weapon because it’s cheaper still for training but also ammunition is super cheap. You don’t need a fletcher — pretty much anyone can case musket balls.
And then there’s the boom and the fire! That morale effect is significant, especially while the technologies are adjacent. Is it interesting in D&D though? Here you have cone-hatted wizards throwing fireballs and disintegrating things. It might be the case that troops just aren’t all that impressed by the flash bang and smoke of muskets. But maybe. And again, cheap.

But do you, Gorgo the dragon hunter need it? Your ammunition is so abstracted that it’s probably not interesting that it’s cheaper. I mean, it’s just you. You’re not outfitting a thousand soldiers. And ease of use? You’re tenth level. You’re already an expert. So who cares?
When a game mostly only models hit and damage it’s tempting to try and model using only those tools. But they aren’t really sufficient and when you go that route you create potentially optimal choices or just wrong results. And when technologies are adjacent or overlapping there isn’t always an optimal choice, especially if you are looking at military technology in the context of personal use (where many of the advantages may be irrelevant).
So instead let’s look at the fact that this just isn’t a military problem and so military technology might not be relevant — the pressures that drive choices are actually very different. My character can afford any non-magical weapon, is facing fearless foes (mostly), has all the training, and can buy ammunition. So how to differentiate?
I would go completely sideways: if the predominant weapon use for adventurers is killing monsters, then what technology would the availability of black powder present that is really good for THAT job? That is, ignore what armies choose. Just look at the core technology. What can you make with that that does YOUR job?
So I’m thinking that instead of looking at military technology let’s look at something more relevant. How about whaling?

I think if I was hunting dragons I would want something with good penetration, massive damage, and if it can also ground my flying target that’s a bonus. What we want is a harpoon with an exploding warhead. You tie off the line and fire with any available technology (very heavy bow, springs, counterweights, gunpowder — it’s not that relevant except to the artist who will make it look cool). It’s a long heavy bolt with a barb. It penetrates and in the best case reduces the dragon’s ability to fly. And then the grenade in the head goes off causing massive damage with an up close and personal explosion of nails and glass.
That’s what my D&D gunpowder weapon would look like. Well, one of them. And it can be modelled with existing tools in D&D. It has a long reload time, requires significant strength. Level of effect (damage? crit?) lets you add effects like GROUNDED or triggering 5d6 of new damage. Easy!
Of course this demands a lot more creative attention. But it feels both more correct and way cooler. To me.
My tinker gnomes, and only my tinker gnomes, can purchase and use an arquebus, which is basically a heavy crossbow reskinned. Just for flavour.
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