Weapon and Armor Rules for Gonzo Post-Apocalyptic and Cyberpunk OSR Games

Let's say you're planning a game that will have a massive variety of equipment– anywhere from daggers and chainmail, to assault rifles and kevlar vests, to powered armor and laser guns.  If so, six things are probably true:

1) You're awesome

2) So is your campaign 

3) Your game will have hundreds of different weapons and armor options in it

4) You want these options to be somewhat balanced, such that plasma guns are better than longbows, but not realistically better– that is, the cowboy will be outmatched against the space marine, but will at least have a chance of doing damage and maybe winning

5) You don't want to individually write up those hundreds of items all at once

6) You want it to be easy to introduce new items as the game goes on, likely including weapons and armor designed by your players

I like the simplicity of systems that say, like, small weapons like daggers do d6 damage, medium weapons like longswords do d8, and large weapons like mauls do d12.  In those systems, you can introduce any new weapon you want and immediately know what its stats should be.

This is the same concept, except a) much more comprehensive for systems where you have wide variances in tech level, and b) uses armor as damage reduction.  

Weapon Types and Damage

Unarmed attacks do d3 damage.

Weapons fall into four sizes: small (dagger, pistol), medium (longsword, machine pistol), large (greataxe, rifle), and heavy (scorpion, mortar, bazooka, heavy machine gun).

In post-apocalyptic games, you have four tech levels: improvised or stone age weapons, low-tech weapons including medieval and wild west stuff, modern weapons of 20th and 21st century tech level like assault rifles and pump-action shotguns, and futuristic weapons like laser guns and lightsabers.

In cyberpunk games these have different names but are mechanically identical: improvised, civilian-grade (mostly legal with permit), military-grade (illegal but widely available), and cutting-edge (not mass-produced yet, the kind of stuff you'll be stealing from corporate research labs).  

A weapon's damage value depends on size and tech level:

Improvised: d4 (small), d6 (medium), d8 (large), d10 (heavy)

Low-tech or civilian: d6, d8, d10, d12

Modern or military-grade: d8, d10, d12, 2d8  

Futuristic or cutting-edge: d10, d12, 2d8, 2d10

Further, a weapon might have certain weapon tags, like it's silent, has an area of effect, needs to take an action to reload after every shot, or uses rare and expensive ammo.  Every positive tag lowers the damage one step, every negative tag raises it a step.  

A few exceptions: Automatic fire; weapons with full auto aren't less powerful, generally.  Reach weapons aren't generally less powerful because greater reach isn't worth as much in these settings.  And versatile weapons (can be used one or two handed) are kinda their own thing; the exact benefits of using two hands may depend on the weapon.  Some tags are also not clearly positive or negative.

Examples:

Broadsword: medium low-tech/civilian melee weapon, d8 damage + STR mod, no tags

Three-section staff: large low-tech/civilian melee weapon, d8 + STR mod  Tag: chain weapon, can ignore shields and be used to entangle enemies

Machine pistol: medium modern/military weapon, d10 damage.  Tags: full auto, versatile (can only use full auto with two hands

Monofilament whip: light futuristic, d10 + DEX mod damage.   Tags: chain weapon (ignores shields), precision weapon (uses DEX instead of STR for damage), dangerous (you hit yourself on a crit fail), powered (needs a battery or power source)

You can adjust somewhat from there, but use those as starting guidelines.  

Armor Types and Values

As mentioned, armor acts as damage reduction rather than preventing you from getting hit.  Shields, in this system, affect your defense (chance to get hit) rather than acting as damage reduction like armor.  

Armor is divided by the type of material used and amount of coverage provided.

Armor Materials

Light primitive, like leather or cloth

Heavy primitive, like steel or iron

Light modern, like kevlar or plastic

Heavy modern, like titanium or modern steel alloys

Light futuristic, like aerogel, genetically engineered spider silk, or carbon nanotube mesh weave

Heavy futuristic, like liquid metal, adamantium, or crystalline metals

Certain mutant animal hides or carapace may count as modern or even futuristic material

Armor Coverage

Partial, less than half the body, like a jacket or vest

Majority, 50-90% of the body, like munition armor 

Total, like plate armor or space marine armor

Armor Values

For armor with partial coverage:

d2- light primitive material
d3- light modern or heavy primitive
d4- light futuristic or heavy modern
d5- heavy futuristic material
d6-
d8-
d10-
d12-

If the armor has majority coverage, raise it one die step.  For total coverage, raise it two die steps.  If it's so heavy you can barely move, like a bomb suit or most powered armor when unpowered, raise it three die steps.  If it's powered armor so heavy you literally can't move when it's unpowered, raise it four die steps.  

Roll your armor die when hit, counting a one as a zero, and subtract that value from the damage received.  

You can mix and match armor pieces to create a composite suit; just figure out which of these categories your personal armor panoply comes closest to.

Bear in mind that armor is never made solely out of heavy materials; there always has to be a light under-layer, and modern armor styles tend to use heavy material only over the most vital areas.  That still counts as heavy, not a mix of heavy and light materials.  

Armor can also have tags, like flame resistant, electrically insulated or conductive, specialized against a certain damage type, etc.

Examples:

Kevlar vest with no plates: light modern material with partial coverage, d3

Spiky leather jacket, chainmail kilt, and soccer shinguards: majority coverage with a mix of light modern, light primitive (biggest piece) and heavy primitive, d4

This new army system: mostly heavy modern materials, majority coverage, d5 with all components, d4 if you strip out some of the extra parts like the face and hip pieces

Concealable form-fitting body armor made of spider-silk weave with aerogel reinforcement over the vitals: light futuristic material with majority coverage, d5

Space marine powered armor like in 40k: futuristic heavy materials, heavy total coverage (heavily encumbered and disadvantage to dexterity tests if it goes unpowered), d10

Bomb suit: Heavy modern materials, full coverage, ones actually count as one, specialized: explosions d5 vs most attacks, 2d4 vs explosions, fire and shrapnel 

What This System Does For You

Nearly unlimited variety without much work.  You can take pretty much any weapon or armor– a chainsaw glaive, spiked hockey pads, homemade grenade launcher, rubber tire lamellar– and immediately know what its starts should be.  

This system also compromises between realism and gonzo– high-tech equipment is significantly better, but not the unsurmountable advantage it realistically would be, so a party armed with revolvers and swords and armored with leather, sports gear and scrap metal can fight robots with laser eyes and have a decent chance of winning.