Armor as Damage Reduction, and Separating Melee and Ranged Defense

I've always been a bit of a realism junkie, so I've always wanted a system that treats armor as damage reduction, and separates out melee and ranged defense.

Shadowrun, where I got my start, actually does this pretty well.  Except that, being Shadowrun, it involves rolling a ton of dice multiple times.  However that's a problem with Shadowrun's overall mechanics rather than this specific idea.

The main problem with armor as damage reduction is that it can cause combat to be way slower and more predictable, with more hits needed to take someone down.  The counterargument here is that that's exactly what armor is supposed to do, so you should compensate by making attacks deadlier overall, but it's absolutely a good thing that well-armored combatants are less likely to be one-shotted than poorly-armored ones.  

Anyway, here's what I came up with.

Armor as Damage Reduction for OSR and D&D-Like Games

Every type of armor has an armor die associated with it.  When you're attacked, roll your armor die.  If you're hit, subtract the amount you rolled from the damage. 

Two caveats, however.  First, ones actually count as zero, to account for the possibility of hitting a gap in the armor.  Second, if you're not wearing a helmet, twos also count as zeroes.  On the other hand, if the armor has literally no gaps whatsoever, ones could count as ones, but you'd mainly see that in sci-fi settings like with space marine armor.  

So, here are the armor values.  Remember that the question of head coverage is left out of this since the purpose of helms is to make twos count as twos.  

Light armor that covers around half the body, like a leather jerkin or padded doublet: d3

Light armor that covers most of the body, like padded armor with long sleeves: d4

Medium armor that covers around half the body, like a chainmail shirt: d4

Medium armor that covers most of the body, like a breastplate plus greaves, vambraces and armored kilt: d6

Heavy armor that covers around half of the body, like half-plate, or is lower quality, like splint mail: d6

High-quality heavy armor that covers almost all of the body, like plate mail: d8

In the post-apocalyptic science fantasy game I have planned, numbers for really high-tech armor will have the potential to go higher than that and I'll probably use a piecemeal armor system, but I haven't worked that out yet.  Umerican Survival Guide does something similar– I only read it after I thought of this idea, and I kind of like it's system but want to simplify it a bit.

One thing I want to note here is that contrary to what you'd intuitively expect, an armor value consisting of two dice doesn't produce results with more of a central tendency than an armor value consisting of one die, because you're already subtracting the armor value from the damage roll.  Like if you look on Anydice, 1d10-2d3 is almost identical to 1d10-1d6.  

So, no reason to overcomplicate this by rolling more than one die for amor.  However if your armor values start going over d12, I would put a 2d8 in there to cover the gap between d12 and d20. 

Separate, Non-Armor-Based Melee and Ranged Defense Values

Here's roughly how I plan to do melee and ranged defense– that is, the DC for an attack roll, which I can't really call armor class anymore since armor no longer contributes to it.  

Melee Defense: 10 + DEX mod + half PC level or monster's hit dice (rounded up, maxing out at +5 at level 9)

My original plan was to instead add a 5E-style proficiency bonus, but I've moved away from that.  If your game is 5E-based, I'd do that instead.  So assuming ability score mods that go from -3 to +3, PC melee defense will range from 8 to 18.  

Ranged Defense: 8 + cover modifier (ranging from 0 to 8)

Cover modifiers: +2 if 30-50% of your body is covered, +4 if 50-80% of your body is covered, +6 if 80-95% of your body is covered.  An additional +2 if it's hard cover, like rock, as opposed to soft cover, like drywall.

If you have full cover but an attacker tries to shoot you through it, you get the same +6 or +8 you'd get for nearly full cover, plus the attacker probably has disadvantage unless they can see you somehow, plus even if they hit, the cover acts as an extra layer of armor, reducing your damage (and ones count as ones).  

So ranged defense ranges from 8 to 16.  You'd just record 8 on your character sheet, since the cover modifier is constantly changing.  I might simplify this system to just two levels of cover plus hard vs soft, meaning cover values only go up to +6.  Not sure yet.    

Also, size modifiers apply to both defense values: +1 for small characters like halflings, -1 for big ones like ogres.  There's a more full list of sizes here.  I would treat any monster bigger than the sizes on that chart as an inverse swarm.      

So one thing you're likely to note here is that melee defense is based on your character's abilities, while ranged defense is based on tactical positioning.  This is deliberate; I want to reward player skills whenever I can, and that's easier to do with ranged combat.

Of course, I'm also going with the rule that attacks against flanked opponents have advantage, and it's easier to get flanked in melee.  So that element of positioning brings player skill into melee combat.  I'll write more about flanking in the future.   

One last thing I want to point out is that this separation of melee and ranged defense was designed for settings where people use guns.  Bullets of course can't be actively dodged, and instead people take cover, so in a modern or future setting there's a clear distinction between how you defend against melee versus ranged attacks. 

In a pre-modern setting where ranged attacks are usually slings and arrows, which can be actively blocked or dodged, and taking cover is less common, there's a lot less of a rationale for separating melee and ranged defense.

What About Shields?

My thinking is that shields would still contribute to defense, rather than acting as damage reduction like armor.  Each shield would have separate melee and ranged defense values– generally smaller shields would be mainly good against melee attacks, and as shields get larger, ranged defense goes up more than melee.  So something like:

Buckler: +1 melee plus can be used as a weapon and qualifies you for two-weapon fighting

Round or heater shield: +1 melee, +1 ranged

Tower shield: +1 melee, +2 ranged, but encumbers twice as much as other shields

Balancing This So Combat Doesn't Take Forever

Another thing that may have occurred to you at this point is that my defense values are about as high as armor classes in other games, yet my use of armor as damage reduction means attacks will do less damage.  So if nothing else changes, combat will take longer.  

The two solutions here would be to lower the defense values, or raise damage.  Lowering defense values leads to more consistent damage, while raising damage leads to less common but harder hits.  

I prefer combat to be deadly and unpredictable, as is the OSR way, so I'd go with raising damage a bit.  

The other thing you could do is have a system for armor degradation where your armor value goes down with repeated hits.  I really want to do this but haven't figured out a way to do it that is both sufficiently simple and realistic for me.