Can a rogue use Two Weapon Fighting to wield a shortsword and a pistol?

Question

My game has renaissance firearms (Chapter 9: DMG, Firearms) and the rogue is proficient with a Pistol (1d10 piercing, 3lb, Ammunition (range 30/90), loading.

He has a custom feat that works similar to Crossbow Expert:

Through a combination of smithing, tinkering and ingenuity, you've discovered how to craft firearms.

You gain proficiency with firearms. You can now ignore the loading property of one-handed firearms. Being within 5 feet of a hostile creature doesn’t impose disadvantage on your ranged attack rolls with one-handed firearms.

He's also attempting to use Two-Weapon Fighting to wield a shortsword at the same time. (Chapter 9: PHB, Combat, Two-Weapon Fighting)

When you take the Attack action and attack with a light melee weapon that you're holding in one hand, you can use a bonus action to attack with a different light melee weapon that you're holding in the other hand. You don't add your ability modifier to the damage of the bonus attack, unless that modifier is negative.

If either weapon has the thrown property, you can throw the weapon, instead of making a melee attack with it.

From what I understand, he cannot dual wield a Renaissance Pistol and a Shortsword as 1) They aren't both light, and 2) They aren't both melee

My question is what should I do to follow the rules more closely, as well as help the rogue out? This style has become part of their character.

I found this for the Crossbow Expert Feat:

When you use the Attack action and attack with a one-handed weapon, you can use a bonus action to attack with a hand crossbow you are holding.

How do I modify this feat to get the two weapon pistol and sword style to fit better?

The character concept is a swashbuckling sword and pistol rogue. I feel that if I just added the above text, the feat would be overpowered.

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Alternatives that I have looked into and that I don't really like (hence this question):

1. I am considering nerfing his pistol from 1d10 piercing to 1d8 piercing and giving it the light property so that he can dual wield it, even though it's not melee.

2. Ignore the fact that it's not melee;

3. Stick to RAW and tell him too bad the game doesn't work that way?

Answer 1

RAW? Not really; "Two-Weapon Fighting" is for melee weapons.

You provided the quote yourself, but I'll add the emphasis:

When you take the Attack action and attack with a light melee weapon that you're holding in one hand, you can use a bonus action to attack with a different light melee weapon that you're holding in the other hand.

Crossbow Expert vs. Your Feat

You've found the nearest equivalent to pistol-and-sword in RAW 5e. You've built some of it into your custom feat, but you left out the part that would allow a pistol-and-sword style.

When you use the Attack action and attack with a one-handed weapon, you can use a bonus action to attack with a hand crossbow (pistol) you are holding.

As a result, you have allowed the less-realistic of the two options. Loading a black powder weapon is a long, complicated, multi-stage process; you have to load the powder, pack the ball, pack the wad, then load the primer. Typically, black powder pistoleros carry more than one gun.

How to solve your problem simply

1. Apply the bonus-action-shot rule from Crossbow Expert.

2. Have your pistolerogue carry more than one pistol.

   Instead of messing with Loading, adjust the custom feat to make drawing and holstering not require an action. Characters with larger numbers of attacks or who expect to maintain fire for multiple rounds will have to purchase multiple weapons. If pistols are suitably rare, that will serve as your balancing factor.

Experience base for this homebrew modification

I've done something similar for a pirate game in D&D 3.5, but the idea applies equally to D&D 5e.

Answer 2

The RAW doesn't allow for dual wielding.

It appears that you understand the rules as written, and exactly how you would be deviating from them.

Alternative within RAW

You could allow the character to hold both weapons in such a way that one or the other could be used without having to drop the other. In that way, they can shoot or melee in a round.

Alternative weapon

Modify the pistol in such a way that it can be used as a melee weapon. Perhaps add a blade to the front. Modify the damage to 1d6 piercing ranged or melee.

Reloading

Either way the character will not be able to reload the weapon without a free hand.