firearms A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes c ...

, freebore (also free-bore, free bore, or throat) is the portion of the

gun barrel A gun barrel is a crucial part of gun-type weapons such as small firearms, artillery pieces, and air guns. It is the straight shooting tube, usually made of rigid high-strength metal, through which a contained rapid expansion of high-pressure ...

between the

chamber Chamber or the chamber may refer to: In government and organizations * Chamber of commerce, an organization of business owners to promote commercial interests *Legislative chamber, in politics * Debate chamber, the space or room that houses delib ...

and the

rifled In firearms, rifling is machining helical grooves into the internal (bore) surface of a gun's barrel for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting to stabilize the proj ...

section of the barrel bore. The freebore is located just forward of the chamber neck and is cylindrical in shape. The diameter of the freebore is larger than the groove diameter of the gun barrel bore so that no rifling is present and projectiles used in the firearm can accelerate through the freebore without resistance.

Location and dimensions

The

is the rearmost portion of a firearm barrel that has been formed to accept a specific

cartridge Cartridge may refer to: Objects * Cartridge (firearms), a type of modern ammunition * ROM cartridge, a removable component in an electronic device * Cartridge (respirator), a type of filter used in respirators Other uses * Cartridge (surname), a ...

or shell. For firearms having a rifled barrel, the bullet typically extends forward from the leading edge of the cartridge case. The portion of the barrel forward of the chamber that provides clearance for the loaded bullet of a cartridge is known as the throat. The throat is composed of both a freebore and a leade. The freebore is slightly larger in diameter than the rifling grooves in order to allow the cartridge to be loaded into the chamber without resistance, as well as to increase the distance the bullet can move before it engages the rifling in the bore. The leade is the tapered section of the throat that transitions in diameter from the freebore to the rifling lands at a shallow angle, typically between 1 and 3 degrees. Freebore length affects the distance the bullet will jump before engaging the rifling when the weapon is fired. Greater freebore length permits bullets to extend further out of the cartridge case to increase space for propellant within the case. Increasing freebore length in order to increase bullet jump is used to delay the onset of resistance from friction and deformation that results when the bullet engages the rifling. Dimensions of freebore length and diameter may gradually increase as hot gas wears the interior barrel surface each time the weapon is fired.

Sources

{{Firearms Firearm components