About Armour

Just as with weapons, D&D has a long tradition of having lovingly-detailed armour lists, and an equally long tradition of players ignoring almost all of these options in favour of a handful of "best" options. And, as with weapons, that's rather pointless - if there are a sixteen options and nobody uses more than about 4, then those other 12 are just taking up space, space that can be better used for something else.

So, what to do about armour?

Benefits and Drawbacks

The obvious thing to do would be to generate a base set of stats for each of the three levels of armour, and then create some benefits and drawbacks for different armours within those categories.

However, in my experience, players consider one (maybe two) things when selecting armour: what AC does this armour give? Any and all other considerations are irrelevant next to how well the armour will protect them from getting hit.

(The other consideration applies to specific characters. Players of rogues will seek out the best armour that doesn't impact their skills - masterwork studded leather or mithral shirts. Bards, in 3.5e, will seek out the best armour that allows them to cast their spells without risk of failure - coincidentally, that same mithral shirt. And so on. Basically, characters will seek armour that does not impact on their other abilities. But, having restricted their choices accordingly, they'll then go for the best total AC, and only the best total AC, that results.)

So, I'm inclined not to bother with benefits and drawbacks for armour. I'm inclined to think they're more hassle that they're worth.

(Now, that said, if there were benefits and drawbacks that did something other than affect AC or skill penalties...)

AC, Dex bonus, and DR

Prior to 3e, D&D armours always granted the character the full use of his Dex bonus to AC. If you were wearing full plate, it was assumed that your greater Dex resulted in you angling the plates to best deflect incoming blows. With 3e of course, limits were placed on how much of a Dex bonus could be applied to AC when wearing each armour. 4e then simplified this - Light armour granted Dex (or Int!) bonus, while Heavy armour did not. (And 5e is marginally more complex again...)

Meanwhile, other games, and optional rules in 3e, allowed for the possibility that armour would not make the character harder to hit but instead would reduce the damage - either with a damage save (the warhammer wargames), damage reduction (WFRP, Star Wars d20 1st Ed), or by adding soak dice (Vampire).

Now, in principle, armour providing damage reduction is indeed the correct solution. In fact, it's likely that armour should actually make the character both harder to hit and reduce the damage taken - full plate armour likely negates a lot of blows entirely, and probably makes a lot of others much less bad.

In practice, Armour as DR sucks. As implemented in 3e (in Unearthed Arcana) it is almost entirely worthless, as characters are now much easier to hit, Fighters use two-handed weapons and maximum Power Attack, and the extra damage just effortlessly burns through any protection from the armour.

Or there's the counter case, where a creature is still hard to hit, you finally manage to land a blow... only to see the DR negate all (or almost all) the damage. Which really sucks.

Finally, allowing Armour as DR then opens up the possibility of armour piercing weapons, which adds a new level of complexity to the game - you roll to hit, you roll damage, you then subtract AP from DR, and then subtract DR from damage...

The bottom line: Armour as DR is, in principle, the right solution... but Armour as AC is the simpler one.

I've also tentatively decided against applying Dex bonuses to AC, except for characters with the "Unarmoured Fighting" feat (which wasn't listed in my previous post on feats :) ). The major reason for this is that I want all a character's defences to be roughly on a par. If Reflex equals half level + class bonus + Dex bonus, and AC equals half level + armour bonus + Dex bonus, then the armour bonuses need to be trivially small, to the point where they're just not worth bothering with.

Proficient and Non-proficient Use

Back when I talked about feats, Captain Ric raised the very valid question of whether it was really right that non-proficient characters get no benefit from wearing armour. Which is fair enough. Coupled with my adjusted thinking on AC, I'm inclined to give all armours a nominal bonus, with higher bonuses for proficient use. To whit:
Light: Proficient +3, Non-proficient +1
Medium: Proficient +5, Non-proficient +2
Heavy: Proficient +7, Non-proficient +3
Light Shield: Proficient +1, Non-proficient +0
Heavy Shield: Proficient +2, Non-proficient +1

Shields Shall Be Splintered

A proficient character carrying a shield, who is subject to a physical attack and who is not surprised, may choose to use his shield to negate the attack. This may be done at any time - before the attack roll, after the attack roll but before the damage roll, or even after the damage roll.

If the character chooses to negate an attack in this manner, his shield is destroyed and can no longer be used.

A character who carries several shields, or who has another character carry them for him, may not use the "Shields Shall Be Splintered" rule. The gods delight in heroes, and so are willing to spare your life in this manner, but if tested they will tire of your presumption and strike you down!

So, then, the armours...

In each grade, there will be four armours, one of each of four types (Leather, Chain, Plate, Composite). In each case, the armours will have exactly the same stats - they give the same AC bonuses, the same Armour Check Penalties, have the same encumbrance. Additionally, with the exception of the composite armours, they'll cost the same. (Composite armours will cost slightly less.)

The key differentiator between the armour types comes when they are made magical - each of the types accept different magical enhancements, so you can get Fortified Plate armours, but not Fortified Chain armours, and so on. Composite armour cannot be made magical (or masterwork, for that matter).

Speaking of masterwork armours, I'm inclined to stick with the 3e model - masterwork armour reduces the ACP by one step, to a minimum of 0. One key difference with 3e, though: armour need not be masterwork before it can be made magical.