The Machinesmith has the ability to create crossbow turrets that has AC 9, Hardness 10, 15 hp, and weighs 30 lbs. When trying to damage this thing, does its hardness effectively give it DR 10/-? Seems like the only way to get around that is have every bad guy inconspicuously be specialized in sundering things or have equipment that passes Hardness of stuff.
Hardness indeed works like DR. The rules on damaging objects are quite clear on how it works. [url]http://www.d20pfsrd.com/equipment---final/damaging-objects[/url]
Ranged attacks by ranged weapons even have a further 50% damage reduction, unless it's a siege weapon doing the ranged attack.
Energy attacks also have a 50% reduction, though subject to GM discretion as some energy types should not get such a penalty. For example fire damage vs a wooden object, like that crossbow turret, should probably do full damage.
So not every bad guy needs to be specialized in sundering things, a fireball can easily lay waste to most of the turrets, as can other fire based attacks (scorching ray for example). Doing 25 damage in one sunder attempt would also destroy the object. A fighter with Power attack, high strength (16-18) and a 2h weapon could destroy the turret reasonably well in one or two hits depending on what bab he has.
The text also specifies that the turret can be disarmed, disable device can also be used to put it out of action. I'd imagine that grappling the turret could also work to prevent it from targeting somebody, but that's up to GM discretion.
So besides sunder you can also disarm it, use disable device or just blow it up with fire. A sneaky rogue could remove the turret from action without destroying it, allowing the player to salvage the turret and use it again later. Looks like plenty of diversity for countering those turrets.
strings have 0 hardness and are the crucial part of the crossbow...
just saying...