Pinfire cartridges are an unusual, obsolete type of early unitary metallic firearm cartridge. Their principle feature was that a firing pin was integrated into each cartridge rather than being part of the gun.
Casimir Lefaucheux developed the first pinfire cartridge in the 1830s, and they enjoyed a brief period of popularity among civilian shooters in the mid-19th century, particularly in France.
The pinfire cartridge attracted little interest from military buyers, who found the idea of ammunition that was "always primed" inherently dangerous (a problem that also dogged needle guns), and baulked at the idea of equipping soldiers with rounds that stood a good chance of discharging while being carried.
With the development of the rimfire and centerfire cartridge, the fate of the pinfire cartridge was sealed: pinfire guns would only ever be curios thereafter, mostly in the form of comically tiny 2mm "matchbox" revolvers.
The pinfire cartridge was an attempt to solve the issues with powder fouling and fragile firing pins that plagued Jean Samuel Pauly's needle gun concept. Rather than burying the primer deep inside the case, it was placed on one side, with an integral firing pin pushing into the case, angled to strike down at it. A pinfire gun therefore always has a small hole at the top of the chamber for the firing pin to project from. At the time they offered a distinct advantage in terms of reloading speed over Cap and Ball revolvers and were more weatherproof than waxed paper cartridges, though a pinfire weapon's ammunition required a certain amount of care in its handling since any accidental strike of the projecting firing pin could potentially set off the round.
Pinfire cartridges were more or less exclusively used in guns with either break-open actions or chambers, either break-action Shotguns, Revolvers or so-called "harmonica guns" where all of the chambers were in a line and passed through the gun's action in a similar manner to a belt feed. These guns required very distinctive hammers designed to press down on the projecting firing pin rather than strike the rear of the cartridge