Arcano-Pneumatic Firearms

Arcano-pneumatic firearms are powerful works of artifice that blur the line between magic and mechanism. They can channel the power of the user's magic to unleash devastating blasts of concentrated arcane energy. Because they lack any other firing mechanism, arcano-pnuematic firearms can only be used by a creature who can cast at least one spell.

Best of Both Worlds

Arcano-pneumatic firearms are on the cutting edge of magic and technology. They combine the magic channeling power of wands with the force channeling power of firearms. As such, they can be used both as a spellcasting focus by a user who is proficient with firearms and as a ranged weapon.

Magical Weapons

When you make a ranged attack with these weapons, or a ranged spell attack using these weapons as your spellcasting focus, you gain a bonus to the attack and damage rolls depending on the rarity of the weapon: +1 for uncommon, +2 for rare, +3 for very rare, and +4 for legendary. Additionally, the damage is considered magical for the purpose of overcoming resistances to nonmagical damage.

Furthermore, because these weapons are powered by magic, they cease to function while under the effects of an antimagic field, however they are not affected by effects like dispel magic, since they merely channel the users magic, rather than produce their own.

Empowered Shots

When you make a ranged attack using these weapons, you can expend a spell slot to increase its damage by one of the weapon's damage die per level of the spell slot used.

Attuned Power

Though these weapons can be used by any spellcaster, their full power comes when handled by an attuned user. While attuned to these weapons, you gain the following benefits:

Its damage type becomes force.

You can add your spellcasting modifier to attack and damage rolls, instead of your dexterity modifier.

You can ignore the Reload property of the weapon. If you load no ammunition in the weapon, it produces its own, automatically creating one piece of magic ammunition when you make a ranged attack with it. The ammunition created by the weapon vanishes the instant after it hits or misses a target.

Special Properties

Weapons with the Special property are described here:

Shotgun. When you would make a ranged attack with this weapon, you can instead choose to fire a burst of energy in a 15-foot cone. All creatures in this area must make a dexterity saving throw with a DC of 8 + your attack bonus with this weapon, taking the shot's damage on a successful save, and half as much on a failed save.

Rifle. The ranges of spells you cast using this weapon as a spellcasting focus are doubled. (Does not apply to spells with a range of Self or Touch)

Clockwork Assault Rifle. When you make a ranged attack against a target using this weapon, you instead fire three shots at that target in rapid succession, making a separate attack roll for each. Attacking in this way only consumes one piece of ammunition.

Star Cannon. When you fire an empowered shot with this weapon, the shot explodes on impact. All creatures within 10 feet of the target must make a dexterity saving throw against your spell save DC, taking 1d10 force damage per level of the spell slot used on a failed save, and half as much on a successful one.

Note: Reload and Misfire Many of these firearms are adapted from Matthew Mercer's Gunslinger class. I also borrowed the reload and misfire mechanics from it. If you do not want to play with those mechanics, simply replace property Reload X with Loading and remove Misfire X. See his class for more details on how these properties work.