firearms A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions). The first firearms originated ...

, 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 arms, 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 ...

between the chamber and the rifled 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 chamber is the rearmost portion of a firearm barrel that has been formed to accept a specific

handgun A handgun is a firearm designed to be usable with only one hand. It is distinguished from a long gun, long barreled gun (i.e., carbine, rifle, shotgun, submachine gun, or machine gun) which typically is intended to be held by both hands and br ...

rifle A rifle is a long gun, long-barreled firearm designed for accurate shooting and higher stopping power, with a gun barrel, barrel that has a helical or spiralling pattern of grooves (rifling) cut into the bore wall. In keeping with their focus o ...

cartridge or

shotgun A shotgun (also known as a scattergun, peppergun, or historically as a fowling piece) is a long gun, long-barreled firearm designed to shoot a straight-walled cartridge (firearms), cartridge known as a shotshell, which discharges numerous small ...

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...

. 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