Percussion Cap (5e Equipment)
From D&D Wiki
Cost: 1 GP per pack of 10
A small metal cap filled with a small charge of an explosive substance for setting off a black powder firearm. Once they are set off, the metal is ripped apart and the charge is expended, leaving them useless and inert. Sudden impact (such as a hammer strike), exposure to heat in excess of 500 degrees Fahrenheit, or another detonation near enough to damage the caps will cause them to explode. Immersion in water will cause them to fail to detonate for up 24 hours while they dry out.
The charges in each cap are extremely small, as they are designed to only be strong enough to set off other, more powerful explosives. Unless they are directly touching a creature, their detonations are loud, but harmless. If they are in contact with a creature when they detonate, they deal 1 thunder damage. If more than one detonate, they deal 1 thunder for every five caps in contact with the creature. Soft objects, such as leather or cloth, can be damaged by these detonations, but hard objects like stone, metals, or hard woods are not.
Percussion caps can be crafted by creatures with proficiency in Alchemist's supplies.