At least two other GMs and I will be running a shared game that uses the optional firearms from the DMG (pg 269). Renaissance arms will be available, and we will be deciding whether we will also make modern arms available. The game will start at level 2, and we currently expect it to reach level 20.
My question is, how competitive will melee martial characters be, compared to ranged firearm users? As I understand it, ranged attackers normally have less DPR but benefit from additional range. Do ranged firearm users outshine melee martial characters in damage? Do they start as competitive but fall off at later levels? Is the increase from firearm damage offset by the increased cost of ammunition or feats? All players who intend to make a ranged character already plan on picking up firearms proficiency.
Knowing this can inform how we award firearms proficiency and determine the costs and availability of different firearms.
I'm looking for answers based on experience running or playing in games where firearms were available.
Best Answer
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Renaissance Firearms are competitive with crossbows (higher damage compared to longer range), before introducing Crossbow Expert. Crossbow Expert relegates renaissance firearms to gimmicks. Melee characters are highly competitive, often dominant, compared to crossbows or these firearms. A Musket deals 1d12 + Dex damage (average 6.5 + Dex) once per round; a Greatsword deals 2d6 + Str damage (average 7 + Str) with each successful attack. That's a huge difference that makes muskets (and pistols) uninteresting for characters with Extra Attack.
So uninteresting that ranged combatants will prefer bows and crossbows over firearms. I played a ranged Fighter in an early 5e game; the DM was excited to have a gun-using hunter, and by level 6 I was using a scavenged longbow as my primary weapon - only the introduction of a home brew repeating firearm^ got that character to use firearms again.
Modern Firearms are a completely different beast. I was looking at a home campaign and wanted to play test the modern firearms; I discovered that they were the best martial weapons in existence. The basic pistol does 2d6 damage (greatsword levels); the shotgun, revolver, and automatic rifle do 2d8 damage (like a War Cleric with Divine Strike); the hunting rifle does 2d10 damage (like Eldritch Blast at level 5); all + Dex because they are ranged weapon attacks. That's average 7 / 9 / 11 + Dex damage per attack. And the Burst Fire ability lets the weapon deal AoE damage, slaughtering swarms.
Introducing Modern Firearms is the death of melee combat as a primary combat style. It is still a viable tactical choice, and for certain classes and builds it is the superior choice, but every competitive Fighter will choose a Ranged combat style and avoid melee-only class options (like Battle Master).
^The weapon dealt 3d8 damage, had Ammunition 6, had Range 120/500, and was magical. It was stupidly powerful as a base weapon.
While not a primary question, this statement needs to be addressed:
The DPR for range attackers is generally the same as melee combatants. The massive +2 attack bonus from the Ranged Combat Style, uniformly d6/d8 weapon dice, ability to add their primary stat to damage, and access to the Marksman feat allows ranged weapon Damage Per Round to be about the same as melee weapon combat (lower damage per hit is offset by a 10% higher hit chance).
The most noteworthy drawback of ranged weapon attacks is a long list of incompatible class abilities.