Firearms are cool. If you don't have guns in your D&D game already then you probably hate freedom or something. These boomsticks are loosely modeled off the ones from Earth's 18th centuries (both 18th centuries don't believe their lies) with some guesstimation and detail-sacrifices for smoother gameplay. Guns are fucking loud and using one in a dungeon is effectively sounding the alarms for everyone in the dungeon and then some.
Muskets are the workhorses of the black powder world. They take a while to reload, but people figured out how to speed the loading process with paper cartridges. Everything you need to fire in a disposable paper case. Muskets fire once every 10 second combat round which starts to push believability, but it's not nearly as bad as heavy crossbows firing once every 6 second combat round looking at you, coast-wizards.
Musket: Cost 60, Weight 105, Damage 1d8, range (50'/100'/300')
Muskets can socket bayonets. This makes the musket shoot at -2, but turns it into a functional melee weapon (as spear).
Musket with Bayonet: 1d6 melee damage, -2 to hit with missile attacks.
Rifles sacrifice ease of loading for much better accuracy (at some point rifle muskets got invented which mucks everything up but let's ignore those for now). They have rifled barrels which spin the bullet and make it much more accurate. For the rifling to work the bullet has to be tight to the barrel which means you've really got to jam it in there. A greased patch of cloth helps. Rifles do not socket bayonets. That's like making a Lamborghini pull a trailer.
Rifle:
Cost 125, Weight 105, Damage 1d8, range (100'/300'/1200')
Blunderbusses work like video game shotguns. If all goes well they fire whatever you pour into the trumpet-shaped barrel in the general direction you're aiming. Ingame that means they hit two targets but have butt-ass range and a smaller damage die. These things were purpose-built to clear goblins out of dungeons which makes their historical popularity somewhat suspicious.
Blunderbuss: Cost 50, Weight 65, Damage 1d6*, can hit a second target, range (10'/15'/30')
Pistols are sidearms. They're often sold in sets of two for dueling, though in rougher parts of the world it's easier to find one without a twin. Count one-handed blunderbusses as pistols even though that might be generous to their effective range.
Pistol: Cost 40, Weight 25, Damage 1d6, range (10'/15'/30')
Hand Dragons are elemental weapons. They are usable by clerics. They function by aerosolizing an alchemical powder stored in a clay disc using gunpowder. It shoots a burst of flame or acid. The spread is not quite wide enough to catch multiple targets. It is up to the player to determine what type of damage the weapon deals before the adventure. The default is fire.
Hand
Dragon: Cost 125, Weight 45, Damage 1d6*, can hit a second target, range
(10'/15'/30')
Black powder era hand grenades are cast iron
spheres about the size of a baseball with a wick sticking out of the top. Same
design as the ones in Looney Tunes or Spy vs. Spy. They do not deal fire
damage, but instead kill through shockwaves and only sometimes shrapnel.
Hand
Grenade: Cost 10, Weight 20, Damage 1d8 (save vs. breath for half), 5' damage
radius, range (10'/30'/50')
*-should probably be 1d4 for balance but IDGAF.
I am not a gunsmith, historian, or academic source. If you cite any of this in a school paper or something you deserve mockery.