Gunpowder and Alchemy

Given my inclusion of firearms I felt I should add Gunpowder to the Craft, Alchemy list...

Gunpowder Cartridge (x10)
Value 1gp; Alchemy Craft DC 5; Weight 1lb

Can be loaded into a firearm along with cast lead bullets (whose value is considered negligible). Unlike other kinds of ammunition cartridges are never re-useable on a miss, magic ammunition is likewise always destroyed and as such comparatively rare.

When ignited outside of a weapon, deliberately or accidentally, each stack of 10 or pound deals 1d6 fire damage to any creature holding or wearing it. The ammunition is ruined.

3lb or more be packed into an explosive charge as a DC10 Craft Engineering check. Failure indicates a failure to detonate while a successful explosion is a 5ft radius blast dealing 3 damage. A single item or creature at the focal point receives 18 damage (reflex half). Each time the amount of explosive is doubled the blast radius increases by 5ft, the blast damage increases by 1 and the damage at the focal point increases by 6. Any affected creature receives a reflex save to halve the damage at a DC equal to the engineer's skill check result when setting the explosive.

Examples
An Arquebusier carrying 20 cartridges for his weapon is targeted by someone speaking Ignan. They receive a Will save against the Ignan effect, if they fail they take 2d6 fire damage from the fireball.

An engineer sets 50lb of Gunpowder as a booby trap. Setting the trap requires a DC10 Craft check. Any creature within 25ft radius of the powder will take 7 damage (reflex for half) except for whichever creature sets off the trap, which instead takes 30 damage (reflex for half).

If the engineer instead used 100lb of powder the blast would be 30ft, blast damage 8 and focal damage of 36.