Often in discussions about firearms and futuristic weaponry in Dungeons & Dragons, the "armor question" often comes up. How does armor class interact with these weapons?
The system I use is based off of the laser weapon vs. armor class values in 1st. edition Gamma World, and an inaccurate interpretation of the armor class vs. firearm rules in the sixguns and sorcery section of the 1st. edition Dungeon Masters Guide. It's a one-size-fits-all solution that I find elegant and workable.
When calculating attacks with firearms or laser weapons, the benefits of armor class are effectively halved, discounting magical protection but including dexterity modifiers (it's hard to dodge a beam of photons or a bullet, but nimble characters are probably somewhat better at not getting shot).
You can either use this as a weapon vs. armor type modifier like the system in the Players Handbook, or just use an alternate Armor Class value against these attacks, as in the below table. This can be further modified by giving exceptional weapons modifiers to attack and damage rolls similar to those of magic weapons, such as a pair of +3 sixshooters forged from the blade of Excalibur. For simple firearms such as muskets and blunderbusses I would not use these modifiers. Weapons such as death rays, lightning emitters, disintegrators, etc. I would either roll attacks vs. AC 10 or involve the target making an appropriate saving throw instead of using any attack rolls.
|Armor Class||Attack Modifier or||Adjusted Armor Class value|