Okay, looking at the rules for Firearms, and then the optional rules for Armor as Damage Resistance, I was wondering about using the two rules together.
Since Firearm attacks resolve against the target's touch AC when the target is within the first range increment of the weapon, does it do the same when using the Defense Score optional rule, since it's similar to touch AC + shield bonus and enhancement bonus to armor?
What about Firearms and Damage Resistance? Since this optional rule makes Guns no different then swords or arrows against armor, would this mean that firearms can instead ignore DR/-?
It's up to your GM. The rules weren't really listed for how they interact.
Personally, I don't care for the touch attack implementation of guns (I understand the realism aspect but it makes it nearly impossible to miss when coupled with the fact that monsters touch AC goes down as CR goes up) and as such I ruled that firearms only are subject to armor as DR rules and do not ignore the DR ever.
Yes, this was to deliberately make guns not very good, though I do tell my players about this rule before play begins.
Guns ignore DR/-? No way.
The word Bulletproof comes from old blacksmiths shooting their armor with a pistol, the dent left as proof that it would stop a bullet, thus bulletproof.
Let it keep the DR/-. After a few levels even the best armor's DR/- is negligible. No point in making life under Armor as DR any harder than it already is.
Guns should not ignore DR/-.
Damage ReductionSome magic creatures have the supernatural ability to instantly heal damage from weapons or ignore blows altogether as though they were invulnerable.
Sometimes damage reduction represents instant healing. Sometimes it represents the creature's tough hide or body. In either case, other characters can see that conventional attacks won't work.
Firearms bypassing armor is somewhat all right. But since DR represents more than just a thick, tough armored hide, giving firearms the ability to bypass it doesn't seem right. Just because you can punch through armor doesn't mean you can stop instant healing.
If you must include a DR piercing ability to firearms, just note that only DR from actual armor can be ignored, not a specific type of DR (like DR/-).