Say a PC has AC/15.....10 base + 3 chain +1 Dex + 1 shield def
Orc warrior swings...roll 14
The PC was able to dance away....
But the PC brings his buckler down in time so that the orcs Warhammer is deflected....
....or
But the PC is a hardy warrior and lets the orcs slashing blade glide along his mail harmlessly....
No matter how the it is envisioned the orc misses, yet how do we decide what part of the AC is the determining factor in the miss, to decide durability damage to items?
If you want to go there, this needs to be under House Rules.
Hit points are non-specific measurements reflecting combat stamina/effectiveness, therefor "hits" and "misses" are likewise non-specific (RAW.)
There may be fan-created ways to reflect what you are looking for - or feel free to develop your own.
thanks
If you start damaging equipment or reducing stats to reflect ongoing damage, you run the risk of creating a death spiral, where it gets harder and harder for the character to recover from what is happening to them or their equipment. It's certainly more reflective of reality but it can be very unfun to have your character reach the point of no return where they are basically doomed before they are actually unconscious or dead according to the standard rules.
There's been a misunderstanding of the rules here.
To damage a creature's equipment, you need to actively target that piece of equipment with a sunder combat maneuver, which can be done in place of any attack, but provokes an attack of opporunity if you don't posses Improved Sunder or Greater Sunder. This is a check of BAB+Strength against a creature's CMD (10+BAB+Str+Dex+Misc. AC bonuses like dodge and deflection or a Monk's Wisdom modifier and unarmoured AC bonus)
If that check is successful, you roll damage as normal, and then apply the hardness of the object (5 is wood objects and hafted weapons, 10 is usually metal objects, even more so for magic items since their hardness and HP is even higher based on their enhancement bonus) against that creature's damage, which works like DR. However, some weapons don't work as well against some materials, and hardness is doubled against those effects or the damage does absolutely nothing. Some damage types might actually bypass that objects hardness due to it's composition. Fire, for instance, might be completely ineffectual against metal or stone, but would do full damage to wooden objects.
A creature's equipment is also damaged on a natural 1 on a saving throw against a damage spell. This is determined based on which piece of the character equipment they happen to be carrying upon rolling the 1, and determined randomly.
Have a look at the Damaging Objects rules if you want to understand this further.
While item hardness and hit points are listed in the rules, those are for deliberate attempts to destroy equipment, notably through the Sunder feat. As mentioned, equipment does not take damage through normal use in combat.
When it's a critical miss (roll of 1) while attacking with a firearm that has the broken condition.
Boom.
What GT-Waifu said.
It is to be assumed that a character using shield or armor to block attacks can do it in a way that doesn't damage them. Unless the opponent targets the item specifically (sunder attempt) the normal usage of an item for defense does not cause damage to the item in question.
Isn't there a fighter feat that allows the fighter to negate a critical hit by giving his shield the broken condition? I suspect that's the closest PF is going to get to this sort of thing.
The short answer is "never".
The slightly longer answer is, "What? You want yet another thing to keep track of?"
Don't forget if you nat1 a save vs a damaging effect then one of your items also takes damage.