Armor has three stats that protect you in different ways, also armor layering

[Greywander]

I just finished watching this video by MrRhexx about his armor resign, and I'm not really sold. The short version is that armor having only one stat is a problem, so his solution to is to give armor only one stat, but now it's damage reduction instead of AC. So I wrote a lengthy comment on the video speculating over a possible better way to handle armor, and I think I found something I really like.

When a creature is attacked, there are four possible outcomes to that attack:

• A miss, where the attack fails to make contact at all and has no effect.
• A glancing hit, where the attack makes contact but the armor causes it to slide off without doing significant damage.
• A direct hit, where the attack hits head-on. The armor can absorb some of the damage, but it's still going to hurt.
• A critical hit, where the attack strikes an unarmored part of the target.

Vanilla actually represents glancing hits pretty well; in fact, that's the primary way that armor protects you. The AC bonus from armor was always meant to represent an attack being deflected by the armor. MrRhexx's proposed change doesn't represent glancing hits at all, since armor no longer improves AC (except magical armor). Vanilla fails to represent direct hits, however, while MrRhexx's damage reduction system does a decent job of modeling a direct hit. All hits in vanilla are "critical" hits, in the sense that armor offers no protection. MrRhexx's homebrew only partly allows critical hits by reducing (but not fully negating) the damage reduction if the attack is made with advantage or if the attacker beats the target's AC by 10.

A miss is solely dependent on dodging the attack, so armor doesn't really affect the miss rate. This means we need three stats that help define the other three types of hits:

• Deflection adds to your AC to represent how well the armor causes blows to glance off.
• Absorption reduces damage taken to represent how well your armor absorbs damage on a direct hit.
• Coverage determine how much the attack needs to beat your AC by in order to bypass your armor's absorption.

For example, let's say my unarmored AC is 12, and I'm wearing armor with 2 deflection. My new AC is then 14, with a roll of 12 or 13 representing a glancing blow. If an attack hits me, my armor has an absorption of 3, so the damage of the attack would be reduced by 3. My armor has a coverage of 4, and 14 + 4 = 18, so if the attacker rolls an 18 or higher they can ignore my armor's absorption and do full damage.

Instead of one piece of armor being strictly better than another piece of armor, we can now have armors that are better at one thing but worse at another. For example, a gambeson (padded armor) would have high coverage, but low deflection and absorption. A brigandine (what studded leather is supposed to be) would have decent deflection, high absorption, but mediocre coverage. So one isn't strictly better than the other. (That said, plate is pretty much the best in all three stats, making it the undisputed king of all armors.)

This then brings us to armor layering. For that, the rules are simple: Only the highest deflection value counts, period. Only one absorption can be used at a time, however the coverage for each piece of armor is checked independently. An attack that beats the coverage of one armor piece might not beat the coverage of another armor piece.

So what we can do is wear both a gambeson and a brigandine. Attacks that get around the brigandine can still be absorbed by the gambeson, essentially giving us the best of both worlds (at the cost of needing to find/buy both armors and being weighed down by both). Also, the armor with the highest deflection might not be the same as the armor with the highest absorption, though in practice you'll probably find these two values correlated.

I don't yet have a list of armors, as this is something I just came up with. I'm also not entirely sure how to determine what armor should have what stats. It seems like there would be a strong link between absorption and deflection, so what are some examples of armors that are good at deflecting glancing blows but bad at absorbing directs hits? Or armors that are great at absorbing direct hits but suck at deflection? What would be the justification for an armor to have high deflection but low coverage, since attacks that don't even hit the armor can't glance off?

On deflection and cloth armors, it's true you probably won't see attacks sliding off a gambeson. But the idea of a glancing hit can still be represented by the attack getting tangled up in the layers of cloth fibers and failing to fully penetrate, which is more likely to happen if the attack strikes at an angle, i.e. basically the same conditions that would cause the attack to glance off of metal armor.

[JNAProductions]

Idea: good.
Execution: not done yet.
Verdict: I like it… but worry a lot about the added complexity. It’s minor, but it’s on every attack. Still… worth exploring. :)

[Greywander]

Lol, yeah, the execution is always the hardest part, isn't it? There is no shortage of good ideas.

It's hard to say how much it will slow down combat, but I think it should be tolerable. Checking a roll against a fixed value is the fastest operation you can do, though I probably should have a spot on the character sheet where you can write down your AC + coverage so you don't have to recalculate it every time. Subtraction takes a little longer, but I think it will help if we keep absorption values fairly low, e.g. 10 or less.

Tentatively, we might say a gambeson has a deflection of 2, absorption of 2, and a coverage of 8. A breastplate might have a deflection of 4, absorption of 8, and coverage of 4. Full plate might have a deflection of 6, absorption of 10, and coverage of 10. Nothing beats plate, but you can see that a gambeson + breastplate would still be highly effective. These are just tentative numbers, though; I'll see if I can hammer out something concrete tomorrow. That plate definitely looks pretty overpowered, but maybe this is just a much needed buff for martials. Though if your enemies are also wearing armor...

Hmm... how should the damage absorption interact with saving throws? Part of the point of saves is having a way to get around high AC. I feel like absorption should either always apply or never apply.

[Old Harry MTX]

The idea is nice, but it seems to me that you add several levels of complexity. Nothing to worry about at my tables, we already have replaced character sheets with spreadsheets, but still it's something not for everybody i think...

Anyway, you should probably starts some betatesting exactly like that, write down a spreadsheet to see how different combination of armors works.

[Ilerien]

I like the concept. 3.5e had a built-in way to distinguish between a miss and a hit absorbed by armor with its AC modifiers of different types which was great. Further granularity might be even more fun.
You might want to steal from Pillars of Eternity and rename "glancing hit" to "graze" just for the sake of brevity. :)

[Analytica]

My favourite thing about this is that you could have different strategies: Dex fighters aim to get criticals so their damage penetrates fully, Str fighters aim to do enough damage even under absorption. Could be woven in well.

[LibraryOgre]

Are you familiar with Hackmaster?

So, all armor has Damage Reduction. Most of it also provides a penalty to your defense (making it more likely you will be hit), and heavier stuff provides penalties to Initiative (how quickly you first react in combat), speed (how quickly you can wield your weapons), and movement (your top speed; not walking, but how fast you can jog, run, and sprint).

Shields, however, have a few differences. They change your defense die (most of the time, you roll a d20p-4; with a shield, you're usually rolling a d20p), add a bonus to defense (about a +6, depending on size), and create a range called a "shield hit"... if, while using a shield, you are missed by less than 10, you instead take a shield hit, which does less damage, and has to get through both your shield's DR and your DR.

Wearing armor becomes a matter of trading agility to get endurance. Using a shield can result in you getting hit more often, but you take a lot less damage for most of those hits. Since damage is tracked, and healed, per wound, smaller hits means back on your feet faster... ten 3 point wounds and you're on your feet in 6 days (or less, with a competent medic). One 30 point wound and you're looking at a year to be fully healed (one day per current point of damage, so 30 days to reach 29, 29 to reach 28, etc., until you've spent 465 days, assuming you don't have a medic).

[Calen]

It seems like there would be a strong link between absorption and deflection, so what are some examples of armors that are good at deflecting glancing blows but bad at absorbing directs hits? Or armors that are great at absorbing direct hits but suck at deflection? What would be the justification for an armor to have high deflection but low coverage, since attacks that don't even hit the armor can't glance off?

A simpler method that still hits most of your points might be to have 2 stats. As you mention absorption, and deflection appear to have a strong correlation most of the time. I'll just call it deflection here.
Any attack below base AC+Deflection misses completely. Deflection would come from unarmored defense, shields, parrying, and maybe armor that could no-sell a hit.
Coverage would be a value above your base AC, any attack that beats deflection but not coverage would deal half damage (like having resistance to the attack, probably write it that you have resistance to BPS attacks. Feats or armor could allow you to add a damage type to that list.)

So a gambeson might have no deflection but a 7 or 8 for coverage. A breastplate and helm might have a 5 deflection but only 3 coverage. Your armor stacking would also work, using the best value of each stat that you have.

Thoughts: Dexterity becomes useful for heavy armor wearers at least until they can get full-plate. The front-line will probably end up getting hit more often but might be taking less damage overall.

[biolante1919]

Absorption and deflection could be the same number, so you get a bonus to armor and an equal damage reduction on most hits. Or theres some automatic relationship between the two.

[Amechra]

Taking a crack at simplifying this... may I suggest the following?

• Wearing armor gives you +1 AC. Shields give you an extra +1 AC.
• Each type of armor has a list of damage types it gives you Resistance to.
• Critical hits bypass Resistance from armor.
• What counts as a critical hit is determined by your armor.

To throw around some numbers pulled out of my hat (using my personal house rule where "medium" armor isn't a thing):

Armor Type	Proficiency Required	Strength Required	AC Bonus	Critical Hit Range	Resistances	Expensive?
Unarmored	---	---	+0	18 - 20	---	No
Light	Light	---	+1	19 - 20	Slashing	No
Shield	Shield	---	+1¹	20	Piercing	No
Heavy	Heavy	15²	+1	20	Slashing + Piercing	No
Plate	Heavy	15	+1	---	Slashing + Piercing	Very Yes

¹ This does stack. Yes, light armor + a shield is pretty much strictly better than just wearing heavy armor — the advantage heavy armor gives you is that it leaves both of your hands free.
² If you get your heavy armor fitted to you, you can reduce the Strength requirement to 13. This is pretty expensive. You can't do this with Plate, which already has to be fitted to you — why did you think it was so expensive?

If you go this route, I'd suggest making it so that Natural Armor, Mage Armor, and Unarmored Defense all count as light armor, with the following extra tweaks:

• Barbarians get to add their Constitution to their AC instead of their Dexterity.
• Spellcasters can end Mage Armor as a reaction to being attacked to make their AC 10+Dex+[CASTING STAT] until the beginning of their next turn (this also replaces Shield).
• Monks get to add their Wisdom to their AC instead of their Dexterity. They also count as using shields if both of their hands are empty (Kensei's just need one hand free if they're using a melee kensei weapon).

[Dienekes]

Taking a crack at simplifying this... may I suggest the following?

Correct me if I’m not reading this right. But as is, doesn’t this just make Dex even more of a godstat as Strength has no way to noticeably effect AC. And bludgeoning becomes indisputably the best damage type.

[Greywander]

Correct me if I’m not reading this right. But as is, doesn’t this just make Dex even more of a godstat as Strength has no way to noticeably effect AC.

On that note, I'm trying to figure out a way to limit the effects of having both high DEX and armor with high deflection. I think heavier armor should still be better on a high DEX character, but having high DEX would make armor less important. But if they just straight up stack, then high DEX + good armor becomes overpowered. What we need is a way to do diminishing returns.

Also, historically soldiers in full plate didn't use shields as often, as the plate provided enough protection that a shield didn't really add much. It was more efficient to free up that hand for a two-handed weapon like a polearm or greatsword. For anything less than plate, though, a shield was one of the most important pieces of protection; a shield and helmet would have made a naked barbarian viable, as those two provide enough protection and the exposed skin allowed the barbarian to stay cool and keep from tiring out as quickly.

Hmm, perhaps deflection doesn't add to your AC, but just sets it to a value, and if your AC from DEX is higher than that, you just ignore the deflection from your armor. But the other two properties of armor would still apply. For shields, they might scale their deflection inversely from your AC, e.g. with low AC the shield provides more deflection. Or maybe AC itself has diminishing returns, e.g. if you're above X value then AC only increases at half the rate, as in a +2 becomes a +1, and above Y value it's a third of the rate, and so on. I'll have to give this some more thought.

[Amechra]

Correct me if I’m not reading this right. But as is, doesn’t this just make Dex even more of a godstat as Strength has no way to noticeably effect AC. And bludgeoning becomes indisputably the best damage type.

Yes and yes... it's a rough draft I pulled out of my butt at 1am where I wanted to avoid formulas, of course it's a little janky. :p

If I were doing this as an actual system overhaul, I'd also suggest making bludgeoning weapons deal lower damage to compensate. Then you'd have a choice between a d6 mace (that's really good at getting through armor) and a d10 sword (which is weak vs. armor).


...

Responding to both Dienekes and the thread at large...

Why not just scrap "Dexterity to AC" entirely and just making your AC something like 13+Proficiency/2 (or whatever ends up giving you nice numbers)? Dexterity is already super overloaded as a stat, after all, so why does it also have to contribute to your Not-Getting-Hit-itude? If you want to pump up an ability score to avoid dying, pump Constitution.

[PhantomSoul]

On that note, I'm trying to figure out a way to limit the effects of having both high DEX and armor with high deflection. I think heavier armor should still be better on a high DEX character, but having high DEX would make armor less important. But if they just straight up stack, then high DEX + good armor becomes overpowered. What we need is a way to do diminishing returns.

Diminishing returns or just a change in role (or ideally both?) -- perhaps Dex's contribution when wearing no Armor is to AC... but in Heavy Armor, it's mitigating disadvantages of that Armor with less or even no effect on AC. That's implicitly already the case if you give Disadvantage to Stealth or Swimming or using Somatic Components or the like, since your bonus helps, but maybe Disadvantage is removed when you hit a certain Dexterity threshold. (In 5e, probably on/off for Disadvantage not a more intuitive or pretty or interesting gradient change.)

Correct me if I’m not reading this right. But as is, doesn’t this just make Dex even more of a godstat as Strength has no way to noticeably effect AC.

The mitigation model might help with that, since stats could mitigate different things... but maybe it could even hide elsewhere (like how Constitution is an intuitive counter to suffering additional effects from massive Damage, which gives it a use even if it's a separate one).

And bludgeoning becomes indisputably the best damage type.

If I were doing this as an actual system overhaul, I'd also suggest making bludgeoning weapons deal lower damage to compensate. Then you'd have a choice between a d6 mace (that's really good at getting through armor) and a d10 sword (which is weak vs. armor).

Just gotta add padded Armor or something! But really, it depends on how things look for non-Armored targets (including Natural Armor and general Monsters); maybe Bludgeoning tends to be good against (Armored) combat-trained targets, but the balance changes depending on the target. (I'll admit that my preference is for some level of predictability from narrative elements and that I waaaaaay prefer having different Weapons or strategies be better in different circumstances.)

[Dienekes]

On that note, I'm trying to figure out a way to limit the effects of having both high DEX and armor with high deflection. I think heavier armor should still be better on a high DEX character, but having high DEX would make armor less important. But if they just straight up stack, then high DEX + good armor becomes overpowered. What we need is a way to do diminishing returns.

Also, historically soldiers in full plate didn't use shields as often, as the plate provided enough protection that a shield didn't really add much. It was more efficient to free up that hand for a two-handed weapon like a polearm or greatsword. For anything less than plate, though, a shield was one of the most important pieces of protection; a shield and helmet would have made a naked barbarian viable, as those two provide enough protection and the exposed skin allowed the barbarian to stay cool and keep from tiring out as quickly.

Well, for one, you could have heavy armor add a higher AC, but only allow half your Dex modifier instead of the full amount.

And for shields, of we’re going historic, a big shields was more unwieldy, slowed you down more, and required more strength to use than anything but the heaviest of plate. So you could play that up a bit.

Hmm, perhaps deflection doesn't add to your AC, but just sets it to a value, and if your AC from DEX is higher than that, you just ignore the deflection from your armor. But the other two properties of armor would still apply. For shields, they might scale their deflection inversely from your AC, e.g. with low AC the shield provides more deflection. Or maybe AC itself has diminishing returns, e.g. if you're above X value then AC only increases at half the rate, as in a +2 becomes a +1, and above Y value it's a third of the rate, and so on. I'll have to give this some more thought.

I’m thinking of it like this:

No armor=Dex
Light armor=Dex+1, slashing
Light Shield=+1, piercing
Heavy armor= Req Str 15, .5Dex +5, slashing and piercing
Heavy shield= Req Str 15, .5Dex+2, slashing and piercing

Penalty is additive from total. So -.5Dex twice is 0 Dex benefit.

If you have no Dex bonus heavy armor and shield is highest at +9
If you have 18 Dex there’s no reason why a heavy armor wearer would want to use a shield. It has no benefit.

Or, I suppose it could be Dex penalties. But I would have to do some more math on that.

Yes and yes... it's a rough draft I pulled out of my butt at 1am where I wanted to avoid formulas, of course it's a little janky. :p

Fair enough. We’ve all been there.

If I were doing this as an actual system overhaul, I'd also suggest making bludgeoning weapons deal lower damage to compensate. Then you'd have a choice between a d6 mace (that's really good at getting through armor) and a d10 sword (which is weak vs. armor).

Not a bad framework. But would probably need to come with an additional change in how damage is calculated. As is the difference is only 2-3 points of damage.

Responding to both Dienekes and the thread at large...

Why not just scrap "Dexterity to AC" entirely and just making your AC something like 13+Proficiency/2 (or whatever ends up giving you nice numbers)? Dexterity is already super overloaded as a stat, after all, so why does it also have to contribute to your Not-Getting-Hit-itude? If you want to pump up an ability score to avoid dying, pump Constitution.

Largely to make ability scores “feel right” as nebulous as that is. But being quick on your feet and agile making you hard to hit is -in my opinion- far more core to the identity of the stat than for example melee damage would be.

[Baniff]

Here's how I do AC. It's not exactly what you are lookong for, but it's pretty simple in play and adds enough granularity to make it worth it I think.
10 + Dex is your "Avoid" range; any attack roll less then this number misses completely.

If an attack is equal to your Avoid + Shield bonus, the attack hits the shield. Shields have a Toughness value. If the attack's damage is = or less than the tougness, then the damage is ignored. If it's above, then the shield is broken.

On top of that is Armor bonus; if the attack roll is higher than Shield bonus, but lower than the Armor, it deals half damage.

If the attack beats the Armor value, it deals full damage.

I think it's easier to explain with an example:

John has a +2 dex, +2 shield with 6 Toughness, and +3 armor.

1- 11 = Miss
12 - 14 = Shield Hit (check damage v tough)
15 - 17 = Armor Hit (half damage)
18 + = Hit (full damage)

Instead of a single AC, everyone writes one of those little charts on their sheets.

I find it fun and useful to simulate certain weapon properties ie; axes deal extra damage to shields, or maces deal extra to plate armor.
Hopefully this made sense and was at all helpful :)

[Amechra]

Not a bad framework. But would probably need to come with an additional change in how damage is calculated. As is the difference is only 2-3 points of damage.

Those 2-3 points of damage do build up over time... but I hear you.

Largely to make ability scores “feel right” as nebulous as that is. But being quick on your feet and agile making you hard to hit is -in my opinion- far more core to the identity of the stat than for example melee damage would be.

Then why not just have Dexterity's sole contribution to combat be AC?

WISDOM: Initiative, attack rolls with ranged weapons.
STRENGTH: Attack and damage rolls with melee weapons.
DEXTERITY: AC, attack rolls with finesse weapons.

Sure, AC would be reduced across the board, but that's why we gave everyone resistances. :p

[PhantomSoul]

Then why not just have Dexterity's sole contribution to combat be AC?

WISDOM: Initiative, attack rolls with ranged weapons.
STRENGTH: Attack and damage rolls with melee weapons.
DEXTERITY: AC, attack rolls with finesse weapons.

Sure, AC would be reduced across the board, but that's why we gave everyone resistances. :p

Or minimally split damage bonuses (always strength) and attack roll bonuses (strength or dexterity, depending on finesse), which is similar to something already hiding in that list. But no, that would obviously be terrible because suggesting this without a full system to balance martials relative to spellcasters is actually anti-martial conspiracy

[Kane0]

Dont forget most monsters dont wear armor but instead have varying amounts of natural AC, so that will have to be factored in somewhere

[Breccia]

I've seen this kind of idea before. Imagine if the shield spell had hit points, basically.

My only concern is, well, not my concern but what I've seen in action: realism adds complexity, and not all players are willing to do that. I personally would love a chart-filled system where, for example, leather/cloth armor had higher absorption against heat and cold; metal armor takes extra damage from acid; and deflection wore off as the armor got dented out of shape. My players would just never use that.

Just make sure you don't make a system that drowns PCs in more stats than they feel like using. I've done that too many times.

[Greywander]

Now that I've had some time to think more on this idea, I wanted to come back to this thread to put my thoughts into words.

First of all, I don't think deflection should stack with DEX (by which I mean it would be more trouble than its worth). This means all armor will probably work a bit more like heavy armor in that it gives you a flat AC value, except you'd have the choice of using your DEX AC instead. This means that low DEX characters would see immediate major improvements after putting on any kind of armor. It also means that, even in the heaviest of armors, you can still benefit from DEX if you push it high enough. It also means there is zero benefit (to AC, at least) to raising DEX if you don't push it higher than your armor's deflection.

I think what makes sense, both from a game design perspective, and also from an appeal to realism, is for DEX builds to be able to achieve the highest AC, while STR builds are worse at dodging but have better damage reduction. Fortunately, this aligns with a lot of our intuition about armor. The heaviest armor should be the best in all categories, meanwhile a DEX build is able to outperform armor in terms of pure AC. The problem is that nothing is stopping the DEX build from just putting on the heavy armor and getting the best of both worlds. So it might make sense to lean a little heavier on encumbrance; DEX builds limit themselves to light armor so they don't take encumbrance penalties, while STR builds can wear the heaviest armor and have carry weight to spare. The only way to get the best of both is to raise both STR and DEX. (Though one concern there is that this only works if you max DEX, but you only need modest STR to wear full plate. It's not balanced between the two.)

Historically, plate was the most protective armor. My first inclination was to give it a deflection of 16, but that's equivalent to a DEX of 22. This goes against the design we established above where DEX builds should have higher AC, while STR builds get better absorption. So I think we just have to remember that 20 DEX is already supernaturally dexterous, and plate armor probably shouldn't be as protective as that (in terms of pure AC, at least). If we give full plate a deflection of 14, then that's still very high, but not as high as 20 DEX. If 14 is the highest deflection, that means we don't have much room to go down for weaker armor, so we'll need to double up a lot. The difference between stronger and weaker armor in the same deflection class would then be down to coverage and absorption.

Speaking of, let's talk about those two. I'd rather keep things simple and streamlined, but I wonder if there's more room for depth in those. For absorption, should it apply equally to all damage types? Historically, different types of weapons were more effective against different types of armor. BPS damage already suffers from being too same-y. What we could do is have some damage types get reduced more than others; either each armor has a high and low absorption numbers, or else we just set the high absorption to be twice the low absorption (or the low to be half of the high). We can then specify for each armor which damage types it is more effective against. For example, mail armor is effective against slashing, while plate is effective against almost everything except bludgeoning, lightning, and psychic. Does that sound like it would be too complicated?

For coverage, there is something I'm considering, but I fear it may be more trouble than it's worth. More coverage means less ventilation, which means you'll tire out quicker. It also gets pretty warm in armor. So perhaps you might add your coverage to any CON saves vs. cold damage or extreme cold, but subtract it from extreme heat or any saves against exhaustion. But honestly that sounds kind of fiddly. Perhaps there's a simpler way to make higher coverage cause your character to tire faster?

One last thing is Unarmored Defense. It could be interesting if monks were the only ones who could push higher than 15 AC by also adding their WIS mod, at the cost of it not working while wearing armor, so no damage absorption for them. By contrast, barbarians might instead get natural absorption equal to their CON mod with a coverage equal to their CON score. It would be less absorption than a lot of armor, but the coverage would be much higher since it's literally their whole body. So you'd at least get that damage absorption reliably on almost every hit you take, except from monsters that are probably too strong for you to be fighting. Could you combine monk and barbarian to create the ultimate defense? Well, barbarian Unarmored Defense might actually work in armor, being treated as an additional layer of armor in case an attack bypasses the coverage of your other armors. If that's the case, stacking it with the monk might also make sense.

That's about all for now. The next step would be to start statting up some armor, but just looking at the deflection values tells me this will need some more thought. Likely full plate and half plate will have a deflection of 14. Breastplates and brigandines 13. Hauberks and haubergeons might be 13 or 12. Gambeson might be 12 or 11. I'm considering if lamellar armor or scale mail should be included. Also, things like leather or hide. For armor in the same deflection class, the major differences would be down to absorption and coverage, and perhaps weight and cost. Armor will also likely be listed as either plate or non-plate (or rigid or non-rigid), and you can only wear one layer of plate/rigid armor, the rest has to be mail or padded or whatever.

I still have no idea how shields will fit into this system.

[Tevo77777]

I have to agree with you. I've seen people do DR for systems that involve firearms, and typically, it's very broken and unrealistic. It also, like you state, does not account for "glancing hits".

IRL, a lot of weapons with good damage, have poor effect against armor.

In wargames, units roll "Saves" to not die, if they get hit. Armor increases this save. Overall, D&D clearly remembers its wargame roots.

However, wargames have "AP" weapons or attacks, which treat armor as being less than it typically is.

-

D20 Modern had this mechanic, but it was kinda weird. Like if you used armor piecing ammo on a target with armor, they became easier to hit and thus damage... However, the ammo always did 1 less damage.

The opposite type of ammo did more damage, but if the target wore armor, they became harder to hit and thus damage.

[Dienekes]

Now that I've had some time to think more on this idea, I wanted to come back to this thread to put my thoughts into words.

Alright, I gotta ask. Are you certain you want to be playing D&D? Because you seem to be trying to recreate Riddle of Steel, but, using as a foundation a system that will be fighting against you every step of the way.

So, I won’t really be commenting on all your ideas here and just make some points on realism.

On plate armor, so, if you’re going for realism here and willing to make a complicated system for it, then plate should still offer some DR against bludgeoning. Not as much as slashing, clearly. But it still helped a lot. Also, metal armor and lightning would be weird. If you are wearing just a breastplate or or just a helmet then being hit by electricity would make you take more damage than otherwise. However, a full harness would have metal from the point of impact to the ground. It would essentially form a faraday cage around you and make you immune.

I normally wouldn’t really bring it up. But since you’re going down the rabbit hole of creating an endurance mechanic just because you think it makes sense even though the only thing in 5e that remotely takes such things into consideration is the rest and exhaustion rules, I’d figure you’d want the information for completeness.

One warning I will give on balance is this:

You also now have a tightrope walk. Because, in general not taking any damage is much better than having some of that damage mitigated. If your plate armor is just reducing some damage by, say 3. That’s really, really good at early levels. And then barely worth mentioning at late levels. I’d gladly swap out 3 DR for a +1 AC. But if you make the mitigation much higher, like 10 DR, maybe that balances better at high levels, but it makes the low levels a cakewalk.

Amechra’s idea to just have Resistance fixes that. But, then you can’t have different degrees of protection per damage type as you said you wanted. Everything would just be resistance or not.

[Breccia]

IRL, a lot of weapons with good damage, have poor effect against armor.

An old show from back in the day did "high-quality katana vs. iron chain mail".

It did not go well for the katana.

https://www.youtube.com/watch?v=RFu11mSutd0

Weapon vs. armor can get as simple (current 5E rules) or as complex as you want, but yeah, the best way to do major damage is to hit the parts of the body where the armor isn't.

I've had only limited success with AP weapons. My last few DM sessions, some weapons had an ability along the lines of "+1 to hit against medium or natural armor, +2 to hit against heavy armor or dragons" or "1d6 damage, increases to 1d8 against light/no armor or natural armor < +3" They haven't worked. Until those new Crit rules kick in, I think my next attempt could be based on crits, which are at least more interesting than +1 to hit/damage.

[Yakk]

Here is an attempt to do this with minimal mechanics.

Defence: Your defence is equal to 10+your proficiency bonus.

Armor: This value adds to your defence. You have Resistance against damage below your Armor value. Critical Hits ignore Armor.

Dodge: As a reaction to being hit, you can add your Dexterity to your Defence. This can cause an attack to miss or be absorbed by Armor. If you have a Shield, you gain +1 to your Dodge.

Light or No Armor: Your first Dodge in a turn does not use a Reaction.

Heavy Armor: Your Dodge bonus is halved. This applies after you add your shield bonus.

Unarmored Defence:
When not wearing armor, Barbarians add their Constitution to their Armor and Dodge.
When not wearing armor, Monks add their Wisdom to their Defence and Dodge.

Bladesong:
When not using medium or heavy armor or a shield, you can add your Intelligence to your Armor and Dodge bonuses.

Shields:
Shields add 2 to your Defence. Magic shields add their bonus to Armor, not defence.

Shield Spell:
Adds +5 to your Defence, but counts as a Shield (the bonuses do not add together). (Note that it interferes with Dodge as well, as both can use a reaction).

Mage Armor:
Adds +3 Armor. Doesn't stack with worn armor.

Barkskin:
Adds +6 Armor, and counts as wearing Medium armor. Don't stack with worn armor.

...

A level 8 Paladin wearing +1 Plate and a +1 Shield. Has 14 dex.

Defence: 15
Armor: 25
Dodge: +1

The same Paladin wearing Half-Plate:
Defence: 15
Armor: 22
Dodge: +3

For every attack, there is a 0.2 chance that the half-plate paladin has a chance to dodge that the full-plate paladin didn't. There is also a 0.1 chance that both will use their reaction to dodge.

(There are two thresholds, one to drop a full hit to an armor hit, the other to drop an armor hit to a defend).

A level 8 Paladin in +1 Studded Leather with 20 dex and a +1 shield.
Defence: 15
Armor: 19
Dodge: +6 (1 free use).

A level 8 Bladesinger with 14 dex, 20 int, mage armor.
Defence: 13
Armor: 21
Dodge: +8 (1 free use)

Level 8 Barbarian with 14 dex 14 con, unarmored
Defence: 13
Armor: 15
Dodge: +4

Level 20 Fighter with 20 Dex, Full plate+3 shield+3, defensive style (+1 DEF)
Defence: 19
Armor: 33
Dodge: +3

Level 20 Barbarian with 24 Con, 20 Dex, +3 shield, unarmored
Defence: 18
Armor: 28
Dodge: +13 (one free)

Level 8 Monk with 18 Dex 16 Wisdom, unarmored
Defence: 16
Armor: 16
Dodge: +7

Level 20 monk with 20 wisdom, 20 dex, unarmored
Defence: 21
Armor: 21
Dodge: +10 (one free)

...

The rogue level 5 Uncanny Dodge feature sort of gets in the way of dodge-as-reaction.

Uncanny Dodge: Starting at level 5, when you use the Dodge action your defence bonus lasts until the start of your next turn. In addition, the next time you are hit by an attack before the start of your next turn, you take half damage from the attack.

that might be too good; it is basically Dodge-to-Defence.

Level 8 Rogue with 20 dex and +1 studded
Defence: 13 (18 really)
Armor: 16 (21 really)
Dodge: +5 (effectively unlimited uses, free)

Level 20 Rogue with 20 dex and +3 studded
Defence: 16 (21 really)
Armor: 21 (26 really)
Dodge: +5 (effectively unlimited uses)

I'm a bit worried if you use Bladesong/Unarmored Defence to super-stack Dodge bonuses then go Rogue 5 to get Uncanny Dodge.

I think if Uncanny Dodge is this "free repeat dodge", then can't have dodge bonuses. Sigh.

Uncanny Dodge: Starting at level 5, you get one additional use of dodge that does not use your reaction. In addition, if you dodge an attack and it still hits, you take half damage from it.

Level 8 Rogue with 20 dex and +1 studded
Defence: 13
Armor: 16
Dodge: +5 (up to 3 uses, halves damage as well)

Level 20 Rogue with 20 dex and +3 studded
Defence: 16
Armor: 21
Dodge: +5 (up to 3 uses, halves damage as well)

A Monk/Rogue becomes strong defensively:

Level 20 Rogue/Monk with 20 dex/wis
Defence: 21
Armor: 21
Dodge: +10 (up to 3 uses, halves damage as well)

Barbarian/Rogue:

Level 20 Rogue/Barbarian with 20 dex/con
Defence: 16
Armor: 21
Dodge: +10 (up to 3 uses, halves damage as well)

Bladesinger/Rogue:

Barbarian/Rogue:

Level 20 Rogue/Bladesinger with 20 dex/int, +3 studded
Defence: 16
Armor: 26
Dodge: +10 (up to 3 uses, halves damage as well)