I've always had a problem with Armor Class. I don't deny that it's a good mechanic to use for figuring combat results and measuring the varying protection that can be provided by different types of armor...but it's still silly. I understand perfectly why variant rules for different types of damage and a more specific Armor Class system weren't implemented into the core rulebooks...after all, combat takes long enough as it is. Adding even more depth to it isn't necessarily going to be something that everyone will love. That being said, I love complexity and realism (to a certain point...) in the games that I run. To that end I've drawn up a set of expanded rules for Armor Class. After a lot of play testing (and a lot of patience on the part of my players) I think I've got 'em just about perfect.
I'm going to start with the AC chain because that's really what started the whole mess. I've always been bothered by the way AC is presented in the core rulebooks. "If you roll this number or less on your attack roll you miss. If you beat it you hurt them." Simple? Yes. Realistic? Definitely not. I can accept that explanation for a defender in leather armor, but consider the case of Bracers of Armor. The description states that the Bracers generate a "magical field of force" which completely encompasses the wearer. If the field has no chinks or breaks into which a weapon can be slipped how, exactly, does a high attack roll hurt them? Does the weapon punch through the field? If so, shouldn't it have its damage reduced based on the strength of the field it passed through? Then there's full plate. That presents a whole other set of problems. I can deal with a rapier finding its way into the slits and joints of plate mail...but what about a greataxe? Surely THAT isn't being deftly guided into breaks in the armor?
My solution to this problem works to a certain extent but it tends to slow things down quite a bit...and it requires a lot of set up work. If you've got ideas on how to do this better I'd be interested in hearing them. My idea consists of two parts: the AC chain, and the armor damage rules.
Part 1: The AC Chain
The AC chain is actually a really simple idea which I still make use of for determining the outcome of attack rolls by both PCs and NPCs. Essentially, an AC chain is a point-by-point chart detailing where a character's total AC comes from. The reason this is important is that it lets you know what (if anything) an attacker did with his attack roll. Basically, you can compare an attack roll with the chart for a given defender and see that the attacker completely missed his target, or the defender dodged out of the way, or the attacker's claws raked across the front of the defender's breastplate. The AC chain itself is created simply by applying a ranking system to the various AC bonuses a character can receive. A character with every type of bonus (that I can think of right now) would look like this:
Base AC: A number in this range misses without the defender having to take any action.
Luck/Divine Bonus: Essentially an extension of Base AC. An attack roll that falls in this range requires no action on the part of the defender to miss.
Dex/Dodge Bonus: This attack would've struck the defender had he not been nimble enough to get out of the way.
Shield Bonus: This attack came too quickly for the defender to get out of the way, but slowly enough that he was able to block with his shield.
Armor Bonus: This attack gave the defender no chance to protect himself. All that saved him from damage was his armor.
Nat Armor Bonus: This attack bypassed all other defenses and was only stopped by the defender's natural toughness.
Thus, a paladin with a few magic items wearing full plate would look like this:
An attacker who rolls a 15 will strike the paladin's shield, while a 17 would strike the paladin's armor. The net effect is the same as the regular AC rules, but it can help players (and the DM!) to visualize how a combat is unfolding.
Part 2: Armor Damage
Ever noticed how almost no one ever chooses to wear heavy armor? After all, why should you when you can receive the exact same protection by having a high Dexterity score and wearing light or no armor? Why burden yourself with 40-plus pounds of dead weight? It's because of this question (and a wistful urge to go back to the days when playing a knight in shining armor was still cool) that I've tried to even out the playing field between heavy and light armors. Be warned, however, that the following variant rules get pretty complex.
First, assign a hardness to each type of armor based upon its material composition. I strongly recommend using hardness 1 for leather and like materials and a hardness of 5 for steel. I know this doesn't match up with the hardnesses presented in the various core rulebooks but trust me, hardness 10 on full plate leads to absolutely ridiculous battles. For magical armor, add 1 to the hardness of the armor for every point of enhancement bonus.
Second, assign a damage threshold to each type of armor based upon its material composition and its construction. Damage threshold represents how many HP from a single blow a piece of armor can absorb before it is breached. I recommend using twice the armor's hardness for this value. Thus, leather would have a DT of 2 while steel would top out around 10.
Third, decide how many hit points a given suit of armor should have. The way I liked the most for doing this was to multiply an armor's AC bonus by 10. Thus, full plate has 80 HP, half plate has 70 HP, and so on. For magical armor, add 10 to the HP of the armor for every point of enhancement bonus.
Fourth, decide on a coverage rating for the armor. I've found that coverage ratings work best when you go by thirds of the body. In this way, breastplates and shirts have a CR of 2, shirts and greaves have a CR of 4, and full-body armors like full plate and full chain have a CR of 6. I arrived at these numbers after a lot of play testing. You're obviously welcome to try your own out, but going much higher than this tips the scales way too far in favor of heavy armor.
Finally, total up the AC of the defender and apply the armor's coverage rating to it. An armor's coverage rating can be looked at as a sort of phantom AC bonus that's added to the top of the AC chain. Whenever an attacker rolls higher than a defender's actual AC but below his phantom AC the weapon deals damage directly to the defender's armor and has a chance to punch through to the person wearing it. (Technically the attack should damage the armor on any roll that falls on the Armor Bonus section of the defender's AC chain but this tends to lead to armor falling apart after only a few fights.)
To determine if an attack is capable of punching through a defender's armor roll damage as normal, then subtract the armor's hardness from the damage roll. The resulting damage is subtracted from the HP of the armor up to its damage threshold. Anything left after that is dealt directly to the defender and is then subject to any damage reduction the character would normally be entitled to.
This adds a final category onto the end of our AC chain:
Phantom AC: An attack roll which falls within this category strikes with enough force to damage the armor of the defender and may (depending upon the force of the blow) punch through to damage the defender.
Thus, our paladin from before would have an AC chain that looks like this:
An attack roll of 27 would hit the paladin's armor with enough force to do damage. A damage roll of 16 would have its first 5 points negated by the armor's hardness. The next 10 points of damage would be absorbed by the armor's HP (reducing it from 80 to 70) and the final point would be dealt to the paladin himself. A few more blows like that and his armor will be nigh-unto useless.
Which leads us to the next logical step in this equation. As armor takes damage its effectiveness will obviously decrease. There are any number of different ways to describe this change in game terms, but I think the simplest and most realistic would be to base it off of a rough percentage. When armor reaches 50% of its total hit points reduce its AC bonus by half (rounding up) and apply a –2 to its armor check penalty. When armor reaches 0 hit points reduce its AC bonus by half again (round up; this will result in a net loss of 75%), apply an additional –2 to its armor check penalty (for a total of –4), subtract 2 from its maximum Dexterity bonus, and reduce its coverage rating by 1 step. These penalties represent the loss of mobility and coverage that come from severe damage to a suit of armor.
Yes, this means that a given suit of armor will, in a drawn out fight, be ruined fairly quickly. I recommend allowing PCs to make untrained (or trained, if they’ve got the tools and skills) repair checks. Based upon the amount of time and materials available, I recommend allowing repair checks to fix anywhere from 1 HP per 5 points rolled on a repair check to 1 HP per 1 point rolled on the check. That’s totally a DM-discretion kind of a thing, but I don’t recommend allowing a character to repair more than 50% of a suit of armor’s HP without proper training or tools, and I’d suggest making each check after the first progressively more difficult, forcing untrained characters to seek out the services of an armorsmith when one is available.
This last issue that I’ll address regarding the armor damage rules is one that hadn’t occurred to me until one of my players brought it up in play testing. Under the current AC rules there’s no system in place for layering armor, but with armor damage rules in effect the practice becomes much more tempting. Here’s my take on it.
First off, common sense should rule the day. You can’t wear a breastplate under a suit of full plate, but you could wear a chain or leather shirt. Even if you could, the added weight of the second suit of heavy armor would essentially immobilize most characters. To that end, I recommend allowing only light armors like padded, leather, and chain shirts to be worn underneath other armor (I would also disallow wearing 2 suits of light armor…no padded-beneath-leather combos). Normal bonus-stacking rules apply…which is to say, they don’t. A person wearing a leather shirt under half-plate would use the armor bonus from the half-plate alone. Similarly, the phantom AC bonuses from the two suits of armor overlap rather than stacking. Armor check penalties should stack and then have an additional –2 added to them. The maximum Dexterity bonus of the most restrictive armor should be used and then reduced by 2. This means that half-plate over leather provides the following stats: AC 7 and Max Dex –2. The benefits of wearing layered armor come into play when the defender’s armor suffers a hit. Let’s go back to the example of the paladin used above, but this time we’ll say he’s wearing leather armor under his full plate. His armor stats would thus be AC 8, Max Dex –1. Plate: CR 6, Hardness 5, DT 10, HP 80; Leather: CR 2, Hardness 1, DT 2, HP 80. His AC chain now looks like this:
0-9 Base (minus 1 for a low Dexterity)
23-24 Phantom (leather and plate)
25-28 Phantom (plate)
Our paladin is now slightly easier to hit in combat due to his reduced maneuverability; however, if he does take a hit it’s almost guaranteed not to cause him any physical damage. Say our attacker rolls a 24. This strikes with enough force to damage the paladin’s armor. The attacker rolls a 22 for damage. The first 5 points are absorbed by the plate’s hardness, then the next 10 points are dealt to its HP. This means that 7 points of damage made it through the plate armor. Next, the leather’s hardness absorbs 1 point of that damage and then 2 points are dealt to the leather’s HP, leaving 4 points of damage unaccounted for. Our paladin takes a meager 4 points of damage and is now ready to return fire. His armor now has 70 HP (plate) / 18 HP (leather).
Finally, we return to the Bracers of Armor and other similar items and effects like Mage Armor. I recommend treating these effects exactly like enhancement bonuses to normal armor but without the armor to back them up and without a hit point total to subtract damage from. Essentially, the hardness and damage threshold of these types of armor are the same thing. This way, Bracers of Armor +2 would have the following stats: AC +2, Hardness 2, Damage Threshold 4, and CR 6.
Like I said way back at the beginning, these rules are deeply involved. I don’t know how much use you’ll get out of them (especially the armor damage rules), but I’d be interested in hearing your opinions on them. I’m really fond of all of them, but the armor damage rules proved to be a little bit too cumbersome for my particular gaming group. The armor damage / phantom AC rules really add to the way heavy armor plays. In my mind it gives it a lot more value, making it much more realistic. Using these rules a knight in full plate is literally a walking tank…and isn’t that what full plate is really all about?
So what do you think? Good? Bad? Ugly?