Firing pin

A firing pin or striker is part of the firing mechanism used in a firearm or explosive device, designed to ignite combustions/detonations by delivering an impact force to shock-sensitive compounds known as primers. 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) 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]

For equestrian thermocautery, see pin firing.
Cut-away view of an M14 antipersonnel landmine, showing the integral firing pin

Typically, firing pins or strikers are made from steel, aluminum or titanium. However, for specialist applications such as zero metal mines, non-metallic materials are used such as glass ceramic.

Firing pin vs. striker
Two-piece striker (hammer with attached firing pin) on a Smith & Wesson Model 13 revolver

A firing pin is a lightweight part which only serves to transfer the momentum received from a spring-loaded hammer, in the same fashion a punch/chisel will relay the blow from a mallet. A striker is usually heavier and bulkier, and is directly connected to a spring, without needing a separate hammer. Striker mechanisms are generally simpler, since they combine the functions of hammer and firing pin in one piece.[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 a hardened, rounded end that strikes the primer. 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. There is some controversy as to whether or not such firing pins are really necessary, with some claiming them to be weaker than the regular steel ones.

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 in bolt-action rifles, while single-piece strikers are found in 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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References
  1. Charles E. Petty. "XD X-Deelicious!". American Cop. Archived from the original on July 23, 2008.
  2. "SAAMI Glossary, F". SAAMI. Archived from the original on 2008-01-31. Retrieved 2008-02-12.
  3. "SAAMI Glossary, S". SAAMI.
  4. "Definition of 'transfer bar'". MidwayUSA GunTec Dictionary. Archived from the original on 2009-07-16. Retrieved 2008-02-12.
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