So I'm looking at adding Firearms, Explosives, black powder, etc to my low magic campaign, however I don't want these items to be common at all. As a part of this I've decided that such weapons are about as stable (in untrained hands) as juggling nitroglycerin. Which is to say highly likely to explode and very powerful when they do. Casual handling of such items is around 30% + to simply blow up (typically killing low level npcs in the immediate area) and thus most npc's will be too afraid to go anywhere near the stuff if they realize what it is. If a dwarf specifically trained in the use of black powder is within 30 feet to supervise the NPC's there is no risk of detonation (ie the dwarf can hire porters and keep them safe).
In trained dwarven hands the only danger of accidental explosion happens on fumbled rolls (such as when using the black powder to create a land mine style trap explosive or attempting to blow open a locked door).
Black Powder reacts negatively to magic & magic users of all types. 25% chance of failure or accidental detonation around arcane users and 15% chance around divine users each round they are within 20 feet. Alternate: allow 2 "safe rounds" before this effect begins to be tracked. This should be enough to allow safe maneuvering during most fights to not cause problems.
NOTE: in more realistic / "gritty" campaigns anytime that a spell is cast on the dwarf with black powder in his possession there is a chance the spell will accidentally detonate the black powder (5 - 10% chance per level of spell?).
Black powder sitting still (such as in a crate or barrel) is completely inert unless a magic item is placed next to it, or a mage decides to use a large bag of the stuff as a pillow. Sleep tight....
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Dwarves and Black Powder
In my home campaign Dwarves may not be any form of arcane spell caster (divine casters are fine) nor use any magic item which is a form of arcane spell trigger (wand, potion, scroll, etc). On the other hand, they are able to handle black powder safely and thus are the only race allowed the use of such items.
Dwarven Alchemists are explosives experts which can manufacture BP weapons of all types (yes I know they are technically a form of Arcane caster, just go with it). Dwarves are the only race allow to take the Gunslinger class, and are the only ones allowed to take feats and archetypes which involve the use of equipment like cannons, landmines, bombs, guns, etc.
Dwarven Divine casters don't trigger negative reactions from Black Powder until they are within 10 feet and accidental detonation chances drop to 10% chance per round. NOTE: spell casters are NEVER intended to be able to safely use this stuff and thus it is strongly recommended to never allow the risk to accidental detonation to be removed by feats, archetypes, spells, etc when being handled by caster classes.
Non-dwarven alchemist bombs (both equipment and the bomb class feature) are assumed to be alchemical in nature and not black powder explosives.
Goblins (or similar creatures) may at DM's discretion also be able to use these weapons in primitive forms (such as basic bombs).
RP side note: Elves HATE black powder weapons due to their explosions and smell.
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Ok guys there is the basic run down. Please refrain from responses like "But that isn't how it is written in D20 RAW and what about race / group / class / etc XYZ???" Yes I know this is different. That difference is intentional and not an over sight.
All that said: What do you think?
It's pretty much only gunslingers & related archetypes which use guns anyway. You're making it dwarven gunslingers which don't multiclass as spellcasters only; even narrower. Personally I'd try to widen the usefulness of guns rather than narrow it. YMMV.
If guns and black powder are that dangerous to handle then that opens a few assassination possibilities.
Pretty much yeah. As I mentioned, it is a low magic campaign and I want black powder weapons to be rare items with built in answers to the challenge of "why haven't guns become more common, and why isn't everyone using / making bombs?" Because only very few people can do it safely and everyone else is terrified of the things.
Secondly I also don't want spell casters using them.
Lastly, I'd decided years ago that dwarves in my campaign would not trust arcane ("elven") magic, and would in fact be banned from using it. As such I was looking for a way to balance that without completely reinventing the wheel.
I completely agree with you about the vulnerability of the black powder being used against the creators (and those who store) such items. Sending in a saboteur to attack such a cache could make for some high adventures!
Assassins/saboteurs and desperate pickpockets are a danger to gunslingers as you say, but I was thinking of letter bombs, bombs concealed under a coach seat etc. not needing fancy fuses. It works both ways.
Nice! Just mail a package to the mage and wait for them to open it? LOL beautiful idea!
@Scrapper - yeah, that is pretty much the direction I'm going with this.