I'm starting a seafaring game soon (Saltmarsh, etc.) and I want to introduce firearms rules but I am concerned about game balance.
Firearms in the DMG are 1 damage die higher than crossbows. Light crossbow d8 -> pistol d10, heavy crossbow d10 -> musket d12. This is balanced by:
1. Lower range increments
2. They're loud
3. Cost of ammo
4. Cost of the weapons themselves
But for many players the damage die matters more than any of those things. So the only real balancing factor is cost. And, the pistol costs 250 gp and the musket 500 gp -- respectable amounts, analogous to the better armors (splint 200 gp, breastplate 400 gp, half plate 750 gp). So that seems fair to me.
Except, I don't want players to select those guns during character creation as part of an equipment package. It would be like starting with breastplate; you are supposed to work your way up to that. So now I've got three options:
1. Forbid starting with firearms. That's lame, though. If I want firearms in the game, I want players to have them.
2. Reduce the price of firearms. But that would remove price as a balancing factor. (Also, I don't want to change the statistics from the DMG -- it's easier for everyone if they can refer to the DMG or the D&D Beyond for those stats.)
3. Introduce new, weaker firearms that you CAN select at character creation.
I picked option 3. While I was at it, I totally stole [MENTION=6801204]Satyrn[/MENTION]'s idea for shotguns, and used them to create stats for blunderbuss and dragoon gun (historically, it was called a "dragon," but I think that terminology may become confusing). Here's what I wound up with:

Firearms in the DMG are 1 damage die higher than crossbows. Light crossbow d8 -> pistol d10, heavy crossbow d10 -> musket d12. This is balanced by:
1. Lower range increments
2. They're loud
3. Cost of ammo
4. Cost of the weapons themselves
But for many players the damage die matters more than any of those things. So the only real balancing factor is cost. And, the pistol costs 250 gp and the musket 500 gp -- respectable amounts, analogous to the better armors (splint 200 gp, breastplate 400 gp, half plate 750 gp). So that seems fair to me.
Except, I don't want players to select those guns during character creation as part of an equipment package. It would be like starting with breastplate; you are supposed to work your way up to that. So now I've got three options:
1. Forbid starting with firearms. That's lame, though. If I want firearms in the game, I want players to have them.
2. Reduce the price of firearms. But that would remove price as a balancing factor. (Also, I don't want to change the statistics from the DMG -- it's easier for everyone if they can refer to the DMG or the D&D Beyond for those stats.)
3. Introduce new, weaker firearms that you CAN select at character creation.
I picked option 3. While I was at it, I totally stole [MENTION=6801204]Satyrn[/MENTION]'s idea for shotguns, and used them to create stats for blunderbuss and dragoon gun (historically, it was called a "dragon," but I think that terminology may become confusing). Here's what I wound up with:
