touchhole

A touchhole, also known as a vent or priming hole, is a small opening at the breech end of a firearm's barrel or cannon. Its purpose is to allow ignition to reach the main propellant charge within the barrel. Historically, touchholes were a simple drilled hole. During firing, a priming charge, often a finer grain powder, was placed in the touchhole and ignited by a match or flintlock mechanism. This ignition then traveled through the touchhole to ignite the main powder charge, propelling the projectile. The size and shape of the touchhole could influence the speed of ignition and thus the firearm's performance. Modern firearms have largely replaced the external touchhole with internal ignition systems, such as primers in cartridges, but the principle of a channel for ignition remains. Early cannons and muskets relied heavily on well-maintained touchholes for reliable operation. Obstruction or damage to the touchhole could render the weapon inoperable.