Wondrous Item, common
A wooden barrel filled with gunpowder, either for storage, or as a timed explosive (if it has a string charge). It weighs 110 lbs.
Explosion. If a flame comes into contact with the gunpowder, it instantly explodes with a bright flash and loud boom. Each creature in a 20-foot-radius sphere centred on that point must make a Dexterity saving throw. A creature takes 4d6 fire damage plus 4d6 thunder damage on a failed save, or half as much damage on a successful one.
Timer. You can link a line of string to the barrel of gunpowder and set it alight. The longer the string, the more time before the flame reaches it and detonates. 1 ft of string equates to 20 seconds.
Notes: Damage, Combat