If I were a player in your campaign I'd walk around naked with a shield because 15 AC for a naked shield is WAY cheaper than Half Plate and I'd get all of my Dex bonus. Super groovy.

Shields reduce your chance to get hit.

Armor reduces how much you get hurt.

If I adjusted armor in my campaign, Plate would be adjusted as well.

I might go back to a touch AC type system as well.  Not sure.  I do know that any balancing I did would still result in plate being by far the most superior option for absorbing blows over short periods by a large margin, but have it severely hampered by extended use. 

Still considering how I'd work the system.  I do know shields were the go to for protection when heavy armor or no armor was not an option.  The issue with D&D there is there's no facing, which prevents the true restrictions the shield offers.  Lots to work out. 

If going for a more realistic system would likely need to rework more than is worth it.

Quote from Ardenwolf >>

If I adjusted armor in my campaign, Plate would be adjusted as well.

I might go back to a touch AC type system as well.  Not sure.  I do know that any balancing I did would still result in plate being by far the most superior option for absorbing blows over short periods by a large margin, but have it severely hampered by extended use. 

If going for a more realistic system would likely need to rework more than is worth it.

 The only way you could adjust plate AC would be to make it better. It's already good, you don't need to make it better. Lowering its AC maes it the same as lesser armor types.

What do you mean "extended use"? You mean like after 20 rounds of combat the wearer should suffer penalties? That's an unjustified penalty, 20 rounds of combat is only 2 minutes. Any trained fighter in plate (Proficient) can fight for far longer than 2 minutes, otherwise the Battle of Agincourt would have been over in 10 minutes.

Again, if you want more crunchy rules, go play something else instead of trying to hammer D&D into something else.

There is nothing wrong with learning and playing something else. In fact, I would argue that learning other systems and playing other games will be good for your gaming health.

Played many systems.  That said there's no problem with musing over various systems or how one might alter them.  Is how new systems often come about, improvements happen,or often how people come to appreciate the system they have as ideas considered demonstrate the beauty of the simplicity of their current system.

Telling someone to go play something else for simply musing on different ideas, is both rude and uncalled for.  A question if I may ask, do you play in not a single D&D campaign without any form of house rule, or deviancy from the rules?  Would not doing so actually be deviancy by itself, as even in the rules themselves they tell you, that you are not expected to do so?  In fact quite often variable and optional rules are listed along side the base rules.

So on what basis do you base your demand that I go play another system, for simply musing on alternate rules?

The suggestion is warranted because the changes you want already exist in other systems. You don't have to bend D&D to fit into what you want, it's already there for you to play.

Yes, I have homebrew rules in my game but they don't mess with core mechanics like HP, AC, Movement, Actions, Skill Rolls. 

If I wanted skill vs skill to see if an attack hits, I wouldn't break D&D, I'd play something else. If I wanted armor to stop damage rather than reduce chance of being hit, I'd play something else. If I wanted armor to have HP, I'd play something else. If I wanted every character to have random powers I'd play something else. If I wanted characters to have 1 HP or 3 HP (ever) I'd play something else. If I wanted to have segmented movement I'd play something else. If I wanted energy allocation before every turn I'd play something else. If I wanted skill ups and level ups during character creation, I'd play something else. If I wanted to be able to summon a greater demon at 1st level, I'd play something else. If I wanted there to be a difference between physical defense and magical defense, I'd play something else. If I wanted to do away with all the dice except d6s I'd play something else. If I wanted more customization in character creation, I'd play something else.

Yet D&D since 3.5 has had optional rules in main core rule books that mess with all those mechanics.

Also NO game system will be perfect for everyone.  Any game system will be lacking in one place or another.  Just because one system may handle, say armor, better than D&D does not mean it might not handle everything else worse than D&D.

Quote from Ardenwolf >>

Yet D&D since 3.5 has had optional rules in main core rule books that mess with all those mechanics.

Also NO game system will be perfect for everyone.  Any game system will be lacking in one place or another.  Just because one system may handle, say armor, better than D&D does not mean it might not handle everything else worse than D&D.

 Neat! You have piqued my curiosity. I stopped playing at the beginning of 3.5 due to kids and only recently jumped into 5e. How did they then and now get rid of or change AC, HP, Movement, Actions from core? I can't imagine a D&D game without AC and HP... please explain, I'm eager to know.

Generally speaking D&D's appeal is simplicity. Other games have more detail so are more complicated. Some folks see complicated/detailed as less fun or harder to play.

In some versions Armor was separate from AC to a degree, in one version armor acted as a form of damage reduction.  You can see similar things with the heavy armor mastery feat in 5e.  It still had AC, but altered how things worked.  Also 3.5 had some AC quirks that 5e no longer has that I miss to some degree.  For example, 5e had three ACs technically in the main system.  It had AC, which then divided into flat AC and touch AC.  I'm going off much of this by memory so pardon any mistakes.

Your base AC was a number that started from 10 and added dex + armor, natural armor + deflection, + shield.  This was typically the highest AC and applied to any attack which you were prepared for and which was not effective with simply a touch.  This was the most common attack.

Then there was flat AC.  This was 10 and added your armor, natural armor, and deflection, plus shield (though I don't necessarily agree with this one.)  This applied to any attacks that didn't require you to be prepared and/or capable of moving.  This AC still applied while paralyzed or stunned, but had no effect on spells or abilities that relied on simply touching the person.  Flat AC would have no effect against say, rays or touch attacks like shocking grasp.

Last was touch AC.  This was 10 + dex + (wis if an unarmored monk), + deflection.  This applied against standard and touch attacks, basically any attack you avoid by moving.  It had no effect (without special abilities) against any attack by surprise, or when unable to move, such as being paralyzed.

It was a more complicated more nuanced system.  In many ways it was clunky, and I didn't agree with where some bonuses went.  I miss some aspects of it though.  In a way I think 5e went too simplified, and both fail to catch some of what I would like represented.  I enjoy both systems though, and have experimented with multiple optional rules and variations.  Have played several non D&D game systems as well. 

Have had a long career gaming, and have seen many systems grow and evolve.  Is why I enjoy occasionally brainstorming new ideas, or seeing how occasionally Frankenstein ideas from various games together too see what works.  Most brainstorming sessions don't go anywhere, a few do, and some are tried but fail severely.  I most certainly am not going to stop though, and be glad for that, if people didn't do this very thing, there would be no 5e D&D at all, and we'd still be playing 1e.  How exactly do you think game systems evolve?  People pickup various systems, they put out their ideas, and some are picked up and refined by developers, or these people eventually move on to become developers themselves.

I play many systems, there is no perfect one, same as I play many types of video games, etc.  I enjoyed fallout 4, I also enjoyed playing it with many different mods, some which altered to the game drastically.  

As for D&D's appeal being simplicity, it has never been nor is it even close to a simple RPG.  That has never been it's appeal.   There are many far simpler games than D&D on many fronts.  D&D is remarkably complex compared to many systems.  Currently we have a game set in Stars without Numbers.  Making a character in that game is ridiculously simple, the rules are not complex.  It's a fun system and game.  Limited in many ways though.  Another super simple system I've toy with is FATE or it's even simpler version FAE.

Also played in Champions, a stupidly complex game, making a character can take forever, and if not careful it's stupidly easy to break the system.  It's on the other side of the spectrum though.  It's not limited hardly at all, and if creative you can make a character that can do anything your heart desires and can imagine.  I've had fun creating characters and powers in the system, but in play, things tended to break, was too easy to have characters so drastically unbalanced compared to each other in the end, we've ditched the system.  Even when we tried making rules to limit things, they ended up breaking down in time.

I like D&D, it's what I started with, all the way in AD&D 2nd edition.  I played with fricken THAC0.  Played it all sorts of ways, in many incarnations, some which you would barely recognize when comparing to 5e.  I also enjoyed many others, like Shadowrun, GURPS (though very limited experience), Star Wars, and many many more games, including a few LARPing experiences.

D&D has bounced all over from less to more complicated depending on which edition you play, but even 5E is far more complicated than some of the other games I play and have played.  Nothing wrong with toying with the rules of D&D or any other system.  When it works it works, when it doesn't it doesn't, but it doesn't hurt to try, and it's through trial and error that we find even better ways to play.  Trust me, THAC0 sucked.

I think The Chart sucked and nobody I knew used it.

What chart are you talking about?

Point is, nothing wrong with messing with systems.  Besides, no amount of another person brain storming has any affect on how you play your game.  Is not like I'm some kind of authority that can tell you how to play your game, like you seem to think you are to me, telling to ditch D&D and go play something else.  Trying to add a bit of realism can result in some fun adjustments.  For example,

In real life, unlike the movies, subduing people without killing them by knocking them out is dangerous, and often leads to death for the person you're trying to knock out. Yes the idea the batman is not killing anyone is absurd, no matter how good he is at knocking people out, some of them are dying.  As a result, we have a rule in game that, if you're trying to subdue an enemy on your final blow, which the rules allow, but in the process roll a critical hit on that attack, your attempts at subduing fail, and, albeit by accident, you kill your opponent.

This rule has resulted in a surprising number of interesting RP moments.

As for armor, my annoyance is, there are too many ways to be as good as a person in heavy armor, and there's no reason in game to ever take the damn stuff off.  Armor is supposed to be annoying and tedious, but that same trade off is why it's so badass.  I mean seriously, most attacks do shit against people in plate, more people in plate lost due exhaustion and concussion and overheating to actual damage from a weapon.  It should be far superior to any unarmored person, not including temporary magic, etc.   I mean there's a reason knights had squires to help them take armor off and put it on.  When's the last time you remember people rping this annoyance, or getting attacked at night and reminding your fighter or paladin player that he needs to lower his AC for being unarmored? 

Never, why?  Because it's being unfairly restrictive to the fighter while the barbarian and monk enjoy their absurd AC's even while butt naked, even worse, they can do this without even a shield, the go to for many unarmored warrior cultures the world over.  Magic is ok, because it requires a resource to get the same thing.  But monks and barbarians only restriction is, they don't need to be annoyed by expending a resource, aka, need time and help to get prepared and unprepared, or worry about things like exhaustion for sleeping in armor.  So absurdity is the solution, don't think to hard about it, and accept it. 

I'm not actually satisfied with that solution.  I'm not sure what solution I would be satisfied with, haven't really seen it, is why I occasionally brain storm on it. 

I'm of two minds on it really.  Either embrace the idea of the monk and barbarian, but that annoys me too, because well both of them get this special AC to allow them to get good AC's while fulfilling the visual archetype of the characters in story their class represents.  Meanwhile, bards and rogues, and assassins, and spies, and other archetypes are made to wear armor to get the same ACs, and more often than not, for many characters types, that armored visual is just as glaringly off as any armored monk or knighted out barbarian would be.  So they're often left jumping through hoops and relying on magic to get the same AC through items, etc, in order to maintain the same visual.  So solution there, I dunno, pick dex, plus charisma or intelligence, for unarmored AC, and find some other perk for barbs and monks to cancel out the bonus every other class is now getting, give each class a way to go unarmored so everyone can have their visuals?  I mean if realism is not required for barbarians and monks to keep their image, why should every other character be required to sacrifice their image for realism?  In this category, am so sick of many of my bards suffering, for not wanting to cover up so damn much, while barbs and monks can go naked everywhere.

In my other mind, being able to survive and absorb hits like that is what armor is for, even the tribes that didn't have armor, typically used shields, and those who could afford armor did so because it increased survive ability severely.  Those who moved around a lot, especially without horses, rarely wore armor, relying on shields instead, since armor, even a simple gambeson, can be exhausting over long distances, especially in the heat.  Going down this road, leads to lots of it's own problems though.  The more I head down the realism road, the more complications and tedium I see. 

The conflict is visuals verses feel.  And that D&D fails a bit in both categories is I think where the problem comes in.  Since the game tends to encourage feel to some degree by having armors, and enforcing them as important for some classes, while, at the same time, allowing some classes to ditch armor completely so that they may maintain their visuals. 

If playing a character not of the visuals supporting type, I'm left unsatisfied, because I'm left either ditching how I envision my character and wearing armor, while others can get away without it, or sacrificing my visuals something they gleefully have no need to do.

Meanwhile if I'm playing a knight like character, and put all this money into plate, and rp the rules about getting into and out of armor, I'm likewise perturbed over monks and barbarians, who, for free and effortlessly can just run around in their birthday suits and get the same AC. I'm role playing a knight in effing plate, give me some respect, this heavy ass shit isn't made of cardboard, how the hell is some naked barbarian and monk able to survive the same shit and sometimes more?  It's absurd.

So I'm left unsatisfied, as it fails to truly embrace either side.  If it embraced one or the other, I may not mind as much, but instead it's some kind of, not quite satisfying mix, where it pays some attention to realism for some, while disregarding it entirely for others.  I mean if it were purely, this is your AC, everything else is visuals, then, I guess I would be ok...  not really...  I get what they're trying to do.  I just don't think they quite perfected it yet.  So I brainstorm in both directions to try and find that satisfying balance I'm looking for.  Sometimes the best way to find problems is to go the extreme in either direction.  I think part of the issue is, AC is too abstract in what it includes.

Either way, don't particularly appreciate being told to play another game, or people telling that to people.  You know nothing of me, my experiences or my condition, nor anyone else for that matter to know if, A: That's even viable for my situation, or B: My motivations for this brainstorming, or C: My experience with other game systems, or D: Many of the other reasons that are possible.

Don't need thought policing, thanks, I'm not some monster trying to destroy your hobby with an iron fist.  You do not need to try, use, experiment with, or even consider any of my brainstorming.  I do, however, appreciate further brainstorming, or issues with an idea being brought up, that's how ideas get refined, or discarded if they prove unfeasible.

I had the idea that instead of adding to a monk or barbarian's AC I'd rule that the relevant bonus x10 armour hit points. So a barbarian with +3 strength, +1 dexterity, and +3 constitution carrying a shield would have a defence class of 14 and 50 armour hit points. Without the shield they'd have 30 armour hit points.

Haven't given it much in depth thought lately, been very busy, but I've enjoyed reading the responses.

Interesting idea to consider...  How would these armor hit points interact with armor?  Like would a barbarian with armor lose those hit points and suddenly gain them back?  How often would they regain these "temporary" hit points?  Would this be a temp hp mechanic?  Would it stack with or replace other temporary hit points?  If so would barbarians then be able to wear both armor and get these hit points? 

As for shield, considered idea of increasing the AC depending on armor type, but only allowing it to apply to a number of attacks in a round equal to your proficiency modifier except when using the dodge action.

Well the basic idea was that armour had hit points and you'd spend hit dice repairing it during a rest. I'd count the unarmoured boost as a kind of armour, so the monk and barbarian's unarmoured boost would just be... added on to the armour they're wearing? I suppose it could be counted separately if you wanted but I'd probably just have it add on.

And if they weren't wearing any armour... Hm. I suppose I'd let them spend hit dice to "repair" their unarmoured boost. E.g. the barbarian reconnects with spirit animal, the monk spends time marshalling their ki.

The character would still gain hit points at +CON mod per level but you'd only be able to heal naturally by resting or through magical or divine means.

I hadn't considered temporary hit points, but I suppose either way would work. My gut reaction was to give the temporary hit points to the character's "meat" hit points, though.

As for shields, I'd increase the range available starting with +1 for a small wooden shield, maybe giving a bigger shield up to +5 or so, which would translate into 10 to 50 armour points. I'd track those separately and maybe allow a character to user their reaction to interpose their shield to take damage instead of their expensive armour. I'll do some more thinking on it all.

I feel like, unless you get tonnes of magical armour, your armour hitpoints won't scale with your level, so a rogue would still have 110 armour hp at 1st level and if they eventually maybe got studded armour it might go up to 120, but would stay that way for a long time. Do you have a solution to this or do you not think that it is a problem?

How does poison and psychic damage work? With the amount of hit points players get each level, when they come face to face with a green dragon, even if they're 10th level they may get one-shot unless your armour somehow magically absorbs poison damage. What about thunder? Deaf creatures are immune to thunder damage (I think, don't @ me on that), how does that work for armour?

Another thing with this system, healing is going to become a bit redundant unless you can heal your armour's hp with healing word or cure wounds as you'll rarely be getting into your "meat" hit points as you say.

How will mending work? You wouldn't have to spend hit dice and they could just repair little by little. Maybe you could do it in combat and regain a hit of armour hp? This spell makes these sorts of systems a bit annoying sometimes. Perhaps you could have the mending spell's components be consumed upon the casting of the spell so that it isn't over used and they need to find the stones to cast it every time.

What about the durable feat? Would that be able to be applied to armour? What about the heavy armour master feat?

I had a few ideas for this:

If you're really hooked on this armour hp solution, you could do something like getting the AC the armour provides x5 and have a few "milestones" for example, leather armour's milestones would be 11, 22, 33, 44, and 55 at max. Every time you reach one of those milestones you could do something like the rust monster, which every time it hits your armour, it decreases the AC that it provides by one, or some other effect. This could work for Barbarians or Monks by saying that they get tired and can't avoid as many blows as they get more damaged?

Have your armour hit points be the AC your armour provides past 10 and times that by 10. Say, leather armour would provide 10 hp while plate provides 80 hp. And then you could add your proficiency bonus times 10 to your armour hit points? Just so that it changes a little and doesn't stay as static. At 1th level with leather armour you'd have 30 hp with leather while your actual AC is still 11+Dex. I just find the 110 hp for a tiny leather chestplate a bit unrealistic? Maybe you can add your strength/dexterity modifier x10 or x5 depending on the type of armour you're wearing?

Maybe you could do something like, when you are hit, you can choose to move your armour in the way and have your armour take the damage instead of you?

OR! You could try giving players a bit more hp? Or just decrease the dice size? It gets boring after a few levels to just repeatedly adding +2 or +3. Maybe a d6 hit dice turns into a d3 and a d8 becomes a d4 and d10s become d6s and the d12 becomes a d8, as one of the barbarian's strong points is their hit dice and taking that away is a bit hard.
Using this, you could make it so that whenever you take damage that isn't poison or psychic, half of the damage hit you and the other half hits your armour. This might work well with the milestone type I described before, with the armour x5 or might even work with the AC past 10 method.

So how much damage does a short sword do when the rogue has 10 hp and 100 hp of armor?

I'm not trying to be insulting, just suggesting that you should try something that already has the mechanics you're looking for.

Right now it seems like you're building 1e RIFTS or 1e Mechanoids.

No offence taken, Wysperra, but I'm also not going to go try something else.

I suppose d6 plus strength or dexterity modifier, which would be taken from armour hit points unless the attack was a critical hit, when character hit points would reduce.

Hm, critical hits... I'd need to consider changing the extra damage or every critical is going to have a good chance of killing the majority of characters.

I'm not "hooked" on this idea at all, if it doesn't work I'll give it up. I appreciate everything being brought up and I'm going to take it into consideration.