Primer

In firearms and artillery, the primer () is the chemical and/or device responsible for initiating the propellant combustion that will push the projectiles out of the gun barrel.

In early, black powder guns such as muzzleloaders, the primer was essentially the same chemical as the main propellant, but poured into an external flash pan, where it could be ignited by an ignition source such as a slow match or a flintlock. This external powder was connected through a small opening at the rear of the gun barrel that led to the main charge within the barrel. As gunpowder will not burn when wet, this made it difficult to fire these types of weapons in rainy or humid conditions.