The typical firing pin is a thin, simple rod with a hardened, rounded tip that strikes and crushes the primer.
The rounded end ensures the primer is indented rather than pierced (to contain propellant gasses).
Firing pins for centerfire cartridges usually have a round cross-section and their movement is usually through a hole in the breechblock along the axis of the center of the barrel's bore.
Pauly also developed a breech-loading shotgun for his cartridge, using a firing pin and external hammer.
[1] The Dreyse needle gun of 1836 uses a paper cartridge with a priming as part of a sabot which cradles the projectile and is forward of the propelling charge.
The needle-like firing pin projects from the bolt-face and pierces the cartridge when the breech is closed.
[4] The pin needs to be aligned with a corresponding slot in the chamber; a disadvantage compared with rimfire and centerfire cartridges that followed and that are also safer.
[2][5] Early rifle designs that fired metallic cartridges typically used a side-lock mechanism, with the hammer mounted to one side rather than inline with the axis of the barrel.
In the trapdoor Springfield Model 1865 (and similar) the rear of the firing pin tube within the breechblock is angled away from the centerline of the barrel toward the hammer.
That part of the block with the firing pin sits on the centerline of the barrel and strikes the primer.
As the bolt fully closes on the breech the primer of the newly chambered round is struck, causing the cartridge to fire.
[10] In firearms terminology, a floating firing pin is one which is unrestricted by a firing-pin return spring or similar.
When the bolt is pushed forward to close the breech, the striker catch is held by the trigger sear.
In cock-on-open operation, this rotation acts on a cam (similar to the action of a screw thread) which retracts the striker, compressing the cocking spring and holding it there.
Mechanical contact fuzes in explosive ordnance will employ a firing pin or striker to initiate detonation.
In landmines, non-metallic firing pins, made from ceramics for example, may be used to minimise their magnetic signature.