I have a gunslinger player in my game who also invested heavily in craft(alchemy), so he could "invent" the grenades that can be found in the alchemical weapon section of ultimate equipment.
I had him invent them, because guns are so rare that it is nigh impossible to buy one outside of Alkenstar and most people haven't ever heard of black powder as a whole.
Recently, he has made the necessary rolls and built some greades, tested them in combat and of course, the one and only thing happened, that ALLWAYS happens, when you give a P&P player explosives.
He wants to build bigger ones that do more damage.
Since that is technically possible and he invented the standard ones, I don't want to outright forbid this, but I also don't want to make it to easy or to game breaking.
So now my question:
What would be the market prices, craft DCs and stats for better/different grenades that you would allow?
I'd allow them, going as far as pulling real grenades into the game (some 6d6 B and P at 30ft radius). But make it a double edge sword. Making explosives in medieval times is no easy thing. I'd add the misfire property to them, like with guns, with the chance to explode right in the face or midair, and tie it to haw good the craft roll was or something.
They already have the "explodes after 1d3 rounds" thing, which I roll secretly so the player doesn't know how to time the throw and is at risk of throwing the grenade to early or to late.
Now if you say 6d6 r30, what would you assume to be the craft DC and price for that?
Right of the top of my head:
Frag - 6d6+6 B/P, 10ft radius full damage, after that 20ft Ref 25 for half, DC to make 35. Price - 250gp. (shards and fragments everywhere!)
Phosphorus - 2d8+8 fire, direct hit - full and ignition for 3d6 rounds dealing additional 1d8 fire damage. 20ft after that Ref 20 for half and ignition for 1d6 rounds. Ref 25 for half damage no ignition. DC to create 35. Price - 300gp. (not to mention possible poisoning)
Cassette - similar to frag but much bigger range and bleed, 3d6 B/P, 10ft radius full damage and 1d6 bleed, after that 40ft Ref 25 for half and 1d6 bleed. Ref 30 for half damage and no bleed. DC to make 35. Price - 300gp. (broken bones included)
Thermobaric - 10d6+6 B/fire, range 5 radius, half damage for 20ft after that. DC 25 fort or deafened for 1d6 hours. DC to make - 40. Price - 400gp. (also ruptured eyeballs and blood vesicles)
Shaped charge. Explodes in 8 symmetric rays. Each is a ranged touch attack +15 at 6d6+15 damage, ignores DR. Half damage if ray is longer than 30ft. Rays go right through targets. No damage after 60ft. DC to make is 40. Price - 400gp. (leaves holes the size of baby fists in anything)
These are loosely based on real world had explosives that deal damage. All variables are up to you. Especially prices. These can be game changers at low levels.
IRL grenades are very deadly. With huge effective ranges and possibilities for destruction. A poor throw of granade will get not only your enemy killed, but also you.
Roll 1d6
1-3 Explodes after 1d4-1 rounds. In result of 0, roll again. Another 0 means it will explode on hand.
4 Ignites after 1d4-1 rounds. If someone is holds it, can use as it burnings hands spell for 1 round/dice of damage. Anyone trying to pick it up have to success in Ref save or get burned.
5 Creates smokescreen with stay 2 round per dice of damage.
6 The fire is quenched. You may try again when you are sure it wont explode on your hands.
Going to be honest, compared to the primitive grenades in Ultimate equipment I think those are a bit much (Most of those stats are better then the modern grenades in d20 modern).
Remember, black-powder is the only explosive he has to work with (We aren't talking C4 here). We aren't talking modern chemistry here. He also is restricted by volume, he can't make a "Bigger" grenade and still be able to throw it any reasonable distance.
For, an Improved Fuse Grenade I think I would do something like this.
Improved Fuse Grenade: Fuse 1d4-1 rounds (A result of 0 explodes on impact), Damage 3d6 Bludgeoning, 2d6 Fire. 15 Foot Radius Burst (Reflex Dc 15 half), Craft (Alchemy) DC30. Cost 200 gold.
Improved Pellet Grenade: Fuse 1d4-1 rounds (A result of 0 explodes on impact), Damage 1d6 Bludgeoning, 2d6 Piercing, 2d6 Fire. 15 Foot Radius Burst (Reflex Dc 15 half), Craft (Alchemy) DC30. Cost 200 gold.
Include repurcussions for using explosive weapons (friendly fire, civilian casualties, wooden structures burn, loot gets destroyed, cover he could've used to hide from archers gets nuked, cave-ins, etc).
Well, I'm not gonna include anything that's worse than side effects from AOE spells. BUt of course, if he uses a grenade in town, there'l be trouble. But I'm pretty certain that's something the character wouldn't do.