An experimental weapon created by a rising artificer, the Thunderbuss packs a hell of a punch. The standard variant fires pellet sized explosive ammunition that deals 2d8 piercing damage to a target on a successful hit, and 1d8 fire damage to any enemies within 5 feet of the target that fail a dexterity saving throw (DC equal to 8 + your proficiency bonus + your Dexterity modifier).

Improvised Ammo
In a pinch, this weapon can use objects under 2 inches wide as improvised ammunition. Damage is at DM discretion, considering size, weight, shape, shrapnel, and other special effects.

Reloading
You must spend 1 attack or 1 action to reload this weapon after being fired. On a critical hit (d20 roll), the weapon is reloaded instantly without requiring an attack or action.

Explosive Ammunition
If attacks with explosive ammo miss the target, the ammunition fails to detonate and bounces away harmlessly. Be wary that environmental conditions in the area could result in the discarded pellets being detonated and potentially hurt allies or the user. The area of effect is up to DM discretion, and any creature that fails a DC 15 Dexterity saving throw will be caught in the blast, and take 1d8 fire damage x the number of missed attacks within the area of effect.

Misfires
When attacking with this weapon, should the user roll a natural 2 or less (d20 roll), the weapon misfires. The attack misses, and the weapon cannot be used again until you spend an action to try and repair it. To repair your firearm, you must make a successful Tinker’s Tools check (DC equal to 8 + misfire score). If your check fails, the weapon is broken and must be mended out of combat at a quarter of the cost of the firearm. Creatures who use a firearm without being proficient increase the weapon’s misfire score by 1.

Upgrades
With additional supplies, Tinkerer's Tools, and a successful skill check, this weapon can be upgraded in the following ways. Upgrades are permanently added, and the damage type can be changed at will on a short rest, on a long rest, or using 10 minutes outside of combat.

Change base damage from piercing to elemental:
Acid - a vial of acid, 150 gold worth of parts
Fire - a fragment of a fire elemental or a bead from a necklace of fireballs, 100 gold worth of parts
Cold - a fragment of a frost elemental or a magic scroll that deals cold damage, 150 gold worth of parts
Thunder - mechanical bellows, 200 gold worth of parts
Radiant - a recently blessed holy symbol, 150 gold worth of parts

Upgrade the weapon to "very rare" quality:
Very Rare Variant - Combine a rare upgrade material from a challenge rating 11 creature and 2000 gold worth of supplies to upgrade this weapon further.

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Firearms are a new and volatile technology, and as such bring their own unique set of weapon properties. Some properties are followed by a number, and this number signifies an element of that property (outlined below). These properties replace the optional ones presented in the Dungeon Master’s Guide. Firearms are ranged weapons.

Reload. The weapon can be fired a number of times equal to its Reload score before you must spend 1 attack or 1 action to reload. You must have one free hand to reload a firearm.

Misfire. Whenever you make an attack roll with a firearm, and the dice roll is equal to or lower than the weapon’s Misfire score, the weapon misfires. The attack misses, and the weapon cannot be used again until you spend an action to try and repair it. To repair your firearm, you must make a successful Tinker’s Tools check (DC equal to 8 + misfire score). If your check fails, the weapon is broken and must be mended out of combat at a quarter of the cost of the firearm. Creatures who use a firearm without being proficient increase the weapon’s misfire score by 1.

Explosive. Upon a hit, everything within 5 ft of the target must make a Dexterity saving throw (DC equal to 8 + your proficiency bonus + your Dexterity modifier) or suffer 1d8 fire damage. If the weapon misses, the ammunition fails to detonate, or bounces away harmlessly before doing so.

Ammunition

All firearms require ammunition to make an attack, and due to their rare nature, ammunition may be near impossible to find or purchase. However, if materials are gathered, you can craft ammunition yourself using your Tinker’s Tools at half the cost. Each firearm uses its own unique ammunition and is generally sold or crafted in batches listed below next to the price.

THIS IS UNOFFICIAL MATERIAL

These game mechanics are usable in your campaign if your DM allows them but not refined by final game design and editing. They aren’t officially part of the Dungeons & Dragons game and aren’t permitted in D&D Adventurers League events unless otherwise stated.

Notes: Reload, Misfire