These rules assume that you're playing an OSR game that uses to-hit rolls; it's easy to hack away from that, if you want, but that's how I usually do it.
If you need a name for these armor rules, call this Damage Threshold Armor, or DT armor.
GOALS FOR THESE RULES:
- Express that armor both makes it harder to land a hit and also can just shrug off small attacks
- Express that maces, hammers, and their ilk don't really care about armor
- Make it easily hackable, and do it without lots of extra dice rolls or tags or anything
Some proper mechanics:
Armor Class and Damage Threshold
Armor has two associated values, which are linked. The first is Armor Class, or AC, which determines how hard you are to hit; this ranges from about 10, which is unarmored, to about 16-17, which is pretty heavily armored indeed. To hit a target, your to-hit roll needs to be above the target's AC. Quite standard, so far.
The second value is Damage Threshold, or DT, which determines how good your armor is negating damage taken from the blows that actually do hit you. DT is equal to AC minus 10; someone at AC 10 has DT 0, AC 13 is DT 3, AC 16 is DT 6, and so on. After hitting a target, to deal damage, your damage roll needs to be above the target's DT; if it's equal to or below the target's DT, the target takes no damage.
As an example, say you hit an AC 13 target with a weapon that deals 1d6 damage, like a dagger. If you roll a 4, the target takes 4 damage; same for a 5 or 6. If you rolled a 1, 2, or 3, though, because the damage is lower than the DT, the target would take no damage.
Helmets & Shields
If you wear a good sturdy helmet, like a sallet or greathelm, your AC and DT increase by 1. If you wield a proper big shield, like a heater or hoplon, your AC and DT increase by 1.
There's an argument to made that each of these should only increase one or other other of AC or DT, and while I think that's valid, I'm a strong proponent of keeping AC and DT linked. You can separate them (more on that in a bit), but I think it's unnecessary.
Slots and Carrying Capacity
Assuming you're using the kinda standard-ish carry capacity system where you have around 8-15ish equipment slots, I use the basic rule of thumb that each DT takes one additional slot. AC 13 / DT 3 would take 3 slots, AC 16 / DT 6 would take 6 slots.
High-DT armor is really, really good under this system, so I feel pretty comfortable in demanding that players spend boatloads of their carrying capacity on it.
A Sample Armor List
A possible armor list:
- Unarmored: AC 10 / DT 0
- Leather Jacket: AC 11 / DT 1
- Gambeson: AC 12 / DT 2
- Brigandine: AC 13 / DT 3
- Maille Hauberk: AC 14 / DT 4
- Full Plate: AC 15 / DT 5
- Shield: +1 AC / +1 DT
- Helmet: +1 AC / +1 DT
Crushing weapons are weapons that derive their damage from huge crushing force, rather than sharp points (like spears) or bladed edges (like swords). Crushing weapons commonly include maces, flails, hammers, mauls, and stones—both the kind hurled from a sling and the kind lobbed off a castle battlement.
When crushing weapons deal damage, if their damage roll is in the upper half of its possible range (such as 4-6 on a d6, or 7-12 on a d12), the weapon always deals damage, regardless of the target's DT. If it rolls in the lower half of its range, it deals damage as normal, based on the target's DT.
For example, if a mace (1d6) was to attack a target with DT 5, if the mace's damage roll was a 4 or 5, it would still deal damage, but a 1, 2, or 3 would not. If the target's DT was 2, anything higher than a 3 would deal damage.
If you're using my combat rules, players can choose to use their weapons in a non-conventional capacity (like mordhau style), you can allow their weapons to deal crushing damage. This gets a little squirrelly with things like, say, ladders, so it's worth discussing ahead of time to work through what the expectations of efficacy there are.
Semi-Optional Rule Because I Haven't Figured Out Quite the Right Balance: Compromised Armor
If you're attacking a target that is in some way compromised—like they're knocked over and lying on the ground, they're paralyzed or tied up, or you're attacking from a hidden position—you ignore the target's DT.
I'd like some kind of middle ground here, since this feels a little too good, but I think it's important to have this kind of caveat, A) because it means you have a solution if you're fighting an ironclad enemy and none of you brought a maul, and B) because the image of a knight in full armor getting tripped up by some goblins and then shanked to death by a dozen daggers is cool.
Like I said, I feel like just straight-up ignoring the DT is maybe a little too powerful, but this is a provisional working rule.
Here's some comparison math of the average damage of dice sizes against various DTs, followed by comparison math of the same, but with crushing weapons.
Damage Dice vs. DT : Average Damage
The equation here is that average damage of 1dX against DT Y, where average damage is Z, is equal to: Z - (Y * 1/X) - ((Y - 1) * 1/X) - ((Y - 2) * 1/X), and so on, until Y is 0. There's a way you can express this using ∑, but it's been too long since I've taken calculus to remember the notation, and I definitely don't know how to put that into blogger.
Point is, the damage drops off slowly at first, and then gets faster; the marginal dropoff increments each time by an amount equal to 1 divided by the die size.
Now, with crushing damage:
Damage Dice vs. DT: Average Crushing Damage
As you can see, this makes crushing weapons pretty darn good. Not unstoppably good, I think (hope), but still quite effective.
What I Like About These Rules
They make armor feel a lot punchier and weightier. A knight clad in full plate will really be able to shrug off the damage, which players love (and hate, when fighting thick monsters). I like that it does this without significantly adding to the either mental math required per roll or the number of dice being rolled. It's still just an attack + damage roll, and then a simple comparison. I also like that it encourages dirty fighting, and it encourages characters to carry ugly, heavy weapons—I like that grungy vibe to my OSR games.
What I Don't Like About These Rules
They add another variable for players to keep track of; it's an easy variable, but it's still a variable. On top of that, I think this system favors crushing weapons a little bit too much; at tables where soft power (see my weapons post) is less encouraged or enforced, there's very little reason to take a sword or axe over a mace. As I said above, I think the compromised armor rule needs a little bit of work; it risks making sneaky-stabby type characters a little too good, potentially.
Still, in the minimal tests I've done so far, these rules have worked well. Let me know how they go for you!