Way back in D&D 3rd edition, I noticed that the weapons table seemed very regular. There were certain patterns that were maintained almost completely across the board. I documented these and wrote them up (still on my very very old pbwiki), to help other people create new balanced weapons.
(Later, one of the 3e designers, Sean K Reynolds, confirmed for me that, while they hadn't quite formalized the rules in the form that I was presenting, my rules were accurate.)
Later, when 5th edition came out, I looked over the weapons again and attempted to extract a similar set of rules. They were a bit more complex, surprisingly, and not quite as regular - 5e seems to have embraced sometimes giving less-effective options for flavor or lower cost (look at the armor table, for instance, phew).
But if you look at the reasonably optimal weapons, the following rules will construct weapons equivalent in power to those on the charts, meaning you can construct your own weapon statlines according to these rules, choosing options as feels appropriate to the weapon, and be sure you're getting a balanced result.
Whenever something refers to increasing or decreasing the die size, use the following progression:
1 -> 1d4 -> 1d6 -> (1d8 or 2d4) -> (1d10 or 2d4+1) -> (1d12 or 2d6) -> 2d6+1 -> 2d10 -> 2d10+1 -> 2d12
(The "or" options are considered equivalent, and either can be chosen at that die size.)
To create a melee weapon, choose a Heft, a Complexity, and an Aspect.
All melee weapons have a 5' range and add Str to attack and damage rolls, unless otherwise specified.
- Light: Weilded in one hand, and small enough to be useful in two-weapon fighting. 1d6 base damage.
- One-handed: Wielded in one hand. 1d8 base damage.
- Two-handed: Must be wielded in two hands. 1d10 base damage.
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Martial: Becomes a martial weapon, requiring special training to use.
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Simple: Becomes a simple weapon, and can be used by most characters.
Comes in two variants:
- Plain: -1 die size.
- Cheap: Extremely cheap to buy (1sp or less), or can be easily crafted by hand by characters with appropriate skills. -2 die size.
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Finesse: Gains [Finesse] quality. Weapon must be Light or One-handed.
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Versatile: Gains [Versatile] quality. Weapon must be One-handed.
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Heavy: +1 die size. Gains [Heavy] quality. Weapon must be Two-handed and Martial.
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Thrown: Weapon must be Simple, and either Light or One-handed. Can be thrown as a ranged attack. (Remember that ranged attacks are made with disadvantage if you're within the threatened range of a hostile enemy.)
Comes in four variants:
- Plain: If Light, +1 die size, 20'/60' range. If One-handed, 30'/120' range.
- Finesse: 20'/60' range, gains [Finesse] quality.
- Versatile: 20'/60' range, gains [Versatile] quality. Weapon must be One-handed.
- Ranged: Actually a Ranged weapon (can't be used in melee, etc.). +1 die size, 20'/60' range, gains [Finesse] quality.
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Reach: Weapon must be Martial. Gains [Reach] quality.
Comes in three variants:
- Finesse: -2 die size, gains [Finesse] quality. Weapon must be Light or One-handed.
- Heavy: Gains [Heavy] quality. Weapon must be Two-handed.
- Mounted: +1 die size. Can be wielded one-handed when mounted. Disadvantage on attacks within 5'. Weapon must be Two-handed.
To create a ranged weapon, choose a Type, a Heft, a Complexity, and optionally an Aspect.
All ranged weapons add Dex to attack and damage rolls.
All ranged weapons impose disadvantage on attack rolls if you are within the range of a hostile creature's weapon. (Ranged weapons can be instead used as improvised melee weapons, removing this penalty when making melee attacks at the cost of acting like plain improvised weapons.)
- Ammunition: Fires a cheap piece of ammunition.
- Loading: Fire cheap ammunition, but it's difficult to load. +1 die size. Can only be fired once per action, regardless of number of attacks.
- Light: Weilded in one hand, and small enough to be useful in two-weapon fighting. 1d4 base damage. 30'/120' range.
- One-handed: Wielded in one hand. 1d6 base damage. 30'/120' range.
- Two-handed: Must be wielded in two hands. 1d8 base damage. 80'/320' range.
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Martial: Becomes a martial weapon, requiring special training to use.
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Simple: Becomes a simple weapon, and can be used by most characters.
Comes in two variants:
- Plain: -1 die size.
- Cheap: Extremely cheap to buy (1sp or less), or can be easily crafted by hand by characters with appropriate skills. -2 die size.
- Heavy: Range becomes 150'/600', and gains the [Heavy] quality. Weapon must be Two-handed.
- [Finesse]: May add either Str or Dex to attack and damage rolls.
- [Versatile]: +1 die size if wielded two-handed.
- [Heavy]: Disadvantage if wielded by Small characters.
- [Reach]: Weapon range becomes 10'.
The weapon list is... let's say "varied" in the quality of its weapons, with some weapons being "good" and others being less optimal, sometimes strictly overshadowed by an otherwise identical option.
The following weapons are constructed as expected by this system:
- Dagger: Light, Simple, Thrown(Finesse)
- Handaxe: Light, Simple, Thrown
- Javelin: 1H, Simple, Thrown
- Quarterstaff: 1H, Simple, Versatile
- Spear: 1H, Simple, Thrown(Versatile)
- Battleaxe: 1H, Martial, Versatile
- Glaive: 2H, Martial, Reach(Heavy)
- Greataxe: 2H, Martial, Heavy
- Greatsword: 2H, Martial, Heavy
- Halberd: 2H, Martial, Reach(Heavy)
- Lance: 2H, Martial, Reach(Mounted)
- Longsword: 1H, Martial, Versatile
- Maul: 2H, Martial, Heavy
- Pike: 2H, Martial, Reach(Heavy)
- Rapier: 1H, Martial, Finesse
- Scimitar: Light, Martial, Finesse
- Shortsword: Light, Martial, Finesse
- Warhammer: 1H, Martial, Versatile
- Whip: 1H, Martial, Reach(Finesse)
- Light Crossbow: Loading, 2H, Simple
- Shortbow: Ammunition, 2H, Simple
- Longbow: Ammunition, 2H, Martial, Heavy
- Hand Crossbow: Loading, Light, Martial
These weapons are simply suboptimal per this system; they can be improved in various ways:
- Club: Light, Simple(Cheap). Missing a Quality.
- Greatclub: 2H, Simple. Missing a Quality. (Should probably be Simple(Cheap) and Heavy, which would move it to "correctly statted".)
- Light Hammer: Light, Simple, Thrown(Plain). Damage too low.
- Mace: 1H, Simple. Missing a Quality.
- Sickle: Light, Simple. Missing a Quality.
- Flail: 1H, Martial. Missing a Quality.
- Morningstar: 1H, Martial. Missing a Quality.
- Trident: 1H, Martial, Thrown(Versatile). Damage too low.
- War pick: 1H, Martial. Missing a Quality.
- Heavy Crossbow: Loading, 2H, Martial, Heavy. Range too low (only 100/400 vs the standard 80/320; the system would bump it to 150/600 to match the longbow).
- Blowgun: Ammunition, 1H, Martial. Damage dramatically too low.
The Dart and Sling are both slightly weird.
Dart is listed as a One-handed weapon (obviously wrong) that's Thrown but Ranged (sole example of this in the game). If you ignore the fact that it's ranged-only, and follow the stat-line literally as a 1H, Simple(Cheap), Thrown(Finesse) weapon, the damage comes out right. But that pretends that being ranged-only is a "free" quality, neither beneficial nor detrimental, when in reality it's generally detrimental, at least with that teensy range. Darts (aka shuriken, kunai, throwing knives) are also absolutely not one-handed weapons. They're smaller than a shortsword, which is a Light weapon; they're generally slightly smaller than a dagger. So, I added Thrown(Ranged), which restricts it to ranged attacks but bumps the die size; pair that with switching the Dart to Light, and the damage comes out right again.
Sling is just slightly too strong. It's an Ammunition, 1H, Simple(Cheap) weapon; that makes it a d6 but with -2 die size, which should drop it to 1. I presume there's an implicit rule that (aside from the incredibly crappy Blowgun) damage can't go below 1d4. That would imply that one could make a Simple(Cheap) dagger, tho, which is identical save that it costs less. So I dunno.