Headspace (firearms)

Headspace (firearms)

In firearms terms, the headspace is the distance measured from the part of the chamber that stops forward motion of the cartridge (the datum reference) to the face of the bolt. Used as a verb, headspace refers to the mechanism by which the correct positioning is achieved. Different cartridges have their datum lines in different positions in relation to the cartridge. For example, 5.56 NATO ammunition headspaces off the shoulder of the cartridge, whereas .303 British headspaces off the rim of the cartridge.

If the headspace is too short, ammunition that is in specification may not chamber correctly. If headspace is too large, the cartridge case may rupture, possibly damaging the firearm and or possibly injuring the shooter.

Headspace gauges

Headspace is measured with a set of two headspace gauges; a "go" gauge, and a "no-go" gauge. Modern headspace gauges resemble the cartridges for the chambers they are designed to headspace, and are typically made of heat-treated tool steel. Both a "go" and a "no-go" gauge are required to headspace a firearm properly.

Headspace gauges are typically used by inserting the gauge into the firearm chamber. The bolt should close and lock on a "go" gauge, and not close on a "no-go" gauge, indicating that the chamber headspace of a firearm is within safe minimum and maximum dimensions, respectively. The force that is applied to the bolt on a bolt-action firearm when making these assessments should only be at normal levels of force; otherwise, an incorrect assessment of headspace may result if the bolt is forced into a position with excessive pressure.

For current or former military calibers, a "field" gauge can also be used. The "field" gauge is designed to take the place of the "no-go" gauge in military firearms, and functions in the same way. Military firearms are designed to withstand higher pressures. As such, a greater tolerance in the firearm's headspace is acceptable, and the "field" gauge takes into account this greater tolerance. "Field" gauges should be used only on military firearms, and not on commercial firearms. Headspacing a commercial firearm with a "field" gauge can create an unsafe condition.

As the "field" gauge takes the place of a "no-go" gauge, any military-surplus gun that locks on a "field" gauge is unsafe to fire, and should be checked by a trained gunsmith.

Guns that fail to lock on the "go" gauge may simply need cleaning, especially at the bolt face, as build-up may occur on this surface and this buildup can cause problems in chambering a round without stressing the brass.

Headspace gauges are designed to indicate simply whether a firearm's chamber is in tolerance. There can be other types of gauges that measure exactly how over or undersize a chamber might be.

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Headspace — can refer to: * Headspace (album) : a debut album by Pulse Ultra * Headspace (firearms) : a distance measured from chamber cartridge stop to the bolt face in firearms. * Headspace (chemistry) : the gaseous constitutes of a closed space above… …   Wikipedia

  • Rim (firearms) — A rim is an external flange that is machined, cast, molded, stamped or pressed around the bottom of a firearms cartridge. The rim may serve a number of purposes, the most common being as place for the extractor to engage. Nearly all modern… …   Wikipedia

  • Cartridge (firearms) — From left: .50 BMG, .300 Win Mag, .308 Winchester, 7.62×39mm, 5.56×45mm NATO, .22LR. A cartridge, also called a round, packages the bullet, gunpowder and primer into a single metallic case precisely made to fit the firing chamber of a firearm …   Wikipedia

  • Handloading — or reloading is the process of loading firearm cartridges or shotgun shells by assembling the individual components (case/shotshell, primer, powder, and bullet/shot), rather than purchasing completely assembled, factory loaded cartridges.… …   Wikipedia

  • Bolt action — The term bolt action refers to a type of firearm action in which the weapon s bolt is operated manually by the opening and closing of the breech with a small handle, most commonly placed on the right hand side of the weapon. As the handle is… …   Wikipedia

  • Delta L problem — The delta L problem (ΔL problem) is a condition that occurs regarding certain firearms chambers and their practical incompatibility with ammunition made for the corresponding chambering. The ΔL refers to a Commission Internationale Permanente… …   Wikipedia

  • Gunsmith — A gunsmith is a person who repairs, modifies, designs, or builds firearms to factory or customer specifications, using hand tools and machine shop tools (such as lathes, milling machines, and grinders).Gunsmiths may be employed in: *factories by… …   Wikipedia

  • Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives — C.I.P. C.I.P. logo Formation 1914 Type standards organization Headquarters …   Wikipedia

  • Accurizing — is the process of improving the accuracy of a firearm or airgun.cite web |url=http://saami.org/Glossary/index.cfm |title=SAAMI glossary |accessdate=2007 08 30] For firearms, accuracy is defined as the ability to hit exactly what you re aiming at …   Wikipedia

  • .40 S&W — Infobox Firearm Cartridge name=.40 S W caption=.40 S W compared to other cartridges (third from right). origin=flagcountry|United States type=Pistol designer=Smith Wesson design date=January 17, 1990 parent=10 mm Auto case type=Rimless, straight… …   Wikipedia