Firing pin

Cut-away view of an M14 antipersonnel landmine, showing the integral firing pin

A firing pin or striker is part of the firing mechanism used in a firearm or explosive device e.g. an M14 landmine or bomb fuze. Firing pins may take many forms, though the types used in fuzes for single-use devices (such as landmines, artillery shells, cluster munitions and grenades etc.) generally have a sharpened point. In contrast, firing pins used in firearms usually have a small, rounded portion designed to strike the primer of a cartridge, detonating the priming compound, which then ignites the propellant (inside) or fires the detonator and booster.^[1][2][3]

Firing pin vs. striker

Hammer with integrated firing pin on a Smith & Wesson Model 13 revolver

A firing pin is a lightweight part, which serves to transfer energy from a spring-loaded hammer to the primer, while a striker is usually heavier, and is directly connected to the spring providing the energy to impact the primer. Striker mechanisms are generally simpler, since they combine the functions of hammer and firing pin in one.^[1]

The firing pin or striker is generally located in the bolt of a repeating firearm. Firearms that do not have bolts, such as revolvers and many types of single-shot actions, generally have a very short firing pin in the frame, or else attached to the hammer itself. These types of firearms are almost never striker fired, as there is insufficient space to house a striker mechanism. Strikers are most commonly found in semi-automatic pistols and bolt-action firearms.^[1]

Firing pin construction

Mauser M 98, bolt and firing pin and safety mechanism field stripped.

The typical firing pin is a small rod with the end that strikes the primer rounded into a hemispherical shape and hardened. The rounded end ensures the primer is indented rather than pierced, as would happen if the firing pin were sharply pointed. Most firing pins have a spring to push them out of contact with the primer, and often will have an integrated passive safety mechanism, such as a block that prevents them from moving forward unless the trigger is depressed, or a transfer bar, also trigger actuated, that must be in place to allow the hammer to depress the firing pin. This safety is in addition to any manually operated safety or safeties that act to block the trigger or hammer.^[4]

Firearms that use long firing pins, such as pistols, will often use a firing pin that is too short to project when depressed flush by the hammer. This type of firing pin, called an inertial firing pin, must be struck by a full fall of the hammer to provide the momentum to move forward and strike the primer. If the hammer is down, resting on the firing pin, it is very unlikely that a blow to the rear will provide enough energy to the firing pin to detonate the primer. Most variants of the M1911 pistol use this type of firing pin.^[2]

Many firing pins are stamped from sheet steel, forming a rectangular cross-section rather than a round one. These will often have a cylindrical section at the front rather than a hemispherical one, and are fairly common in rimfire firearms. Sturm, Ruger, for example, uses sheet metal firing pins in its 10/22 carbine and Mark II pistol.

High performance firing pins are often made from lighter materials than steel, such as titanium. The lighter material increases the speed at which the firing pin travels, and reduces the lock time, or the time from trigger pull to the bullet leaving the barrel. See accurize for more information.

Striker construction

Strikers are basically spring-loaded firing pins, generally of a one- or two-piece construction. In the one-piece striker, the striker is turned on a lathe out of a round bar of metal, much larger in diameter than a firing pin, to provide the mass required to detonate the primer. Two-piece strikers generally consist of a firing pin attached to a heavier rear section—in essence a hammer attached to the base of a firing pin. Two-piece strikers are commonly found on bolt-action rifles, while single-piece strikers are found on pistols, such as the Glock.^[3]

Other uses

Mechanisms involving firing pins can be used also in other pyrotechnical systems, ranging from hand grenades to chemical oxygen generators.

Images

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  Cutaway view of a Russian F1 fragmentation grenade showing firing pin

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  Cutaway view of an M4 anti-tank mine showing integral firing pin

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  Gyata-64 anti-personnel mine

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  PM-79 antipersonnel mine

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  Valmara 59 bounding mine

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  MD-82 mine (Vietnamese near-copy of the M14 mine)

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  Military boobytrap firing device from USSR (normally connected to a tripwire) showing integral striker. The detonator on the end is inserted into a block of explosive e.g. Semtex

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  USSR booby trap firing device—pull fuze: normally connected to a tripwire

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  USSR boobytrap firing device—pressure fuze: victim steps on loose floorboard with fuze concealed underneath.

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  Cross-sectional view of a BLU-43 Dragontooth cluster munition showing firing pin, detonator and adjacent explosive booster charge

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  Cross-sectional view of a Japanese Type 99 grenade showing firing pin.

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  Cross-sectional view of the fuze fitted to a German S-mine

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  Cross-sectional view of an American M2 mine

References

1. 1 2 3 Charles E. Petty. "XD X-Deelicious!". American Cop. 
2. 1 2 "SAAMI Glossary, F". SAAMI. 
3. 1 2 "SAAMI Glossary, S". SAAMI. 
4. ↑ "Definition of 'transfer bar'". MidwayUSA GunTec Dictionary.