Freebore: Difference between revisions
Bentriplett (talk | contribs) I think you mean to write "rotational momentum" not "rotational inertia". Inertia is synonymous with mass, and rotational inertia is similar. Engaging the rifling adds no mass and doesn't change the shape of the bullet enough to change its moment of inertia about its spin axis. Now, even talking momentum instead of inertia, very little of the resistance force acting on the bullet is from change of rotational momentum as a fraction of total resistance due to friction and deformation, so little th |
Bentriplett (talk | contribs) Added a new figure. Reworded to simplify and clarify some of the original points, and to be more in line with the SAAMI glossary of firearms terms. |
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[[File:ChamberIllustration.png|thumb|440x440px|Chamber illustration indicating the various sections of a typical rifle chamber. The freebore is the cyan colored section just ahead of the neck.]] |
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[[Image:Gun barrels cross sectional drawing1.svg|thumb|300px| |
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| ⚫ | In [[firearm|firearms]], '''freebore''' (also '''free-bore''' or '''free bore''') is the forward most portion of the [[Chamber (firearms)|chamber]] of a [[Rifling|rifled]] [[gun barrel]]. The freebore is located just forward of the chamber neck and is usually cylindrical in shape. The diameter of the freebore is always larger than the groove diameter of the gun barrel bore so that no rifling is present and projectiles used in the firearm can move in the freebore without resistance.<ref>{{Cite web|url=https://saami.org/saami-glossary/|title=Glossary – SAAMI|language=en-US|access-date=2019-05-05}}</ref> |
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{{legend|#9292B9|border=1px solid #000|2=Freebore (cross-section of 4 below)}} |
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{{legend|#65B965|border=1px solid #000|2=Rifling (cross-section of 5 below)<br>A = land diameter, B = groove diameter}}]] |
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[[File:Schema patronenlager.png|thumb|Reversed schematic of chamber illustrated in animation below: 1,2 & 3 = chamber]] |
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[[File:Rotating bolt.gif|thumb|Insertion and removal of cartridges from the chamber of a rifle barrel]] |
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| ⚫ | In [[firearm|firearms]], '''freebore''' (also '''free-bore''' or '''free bore''') is the forward most portion of the [[Chamber (firearms)|chamber]] of a [[Rifling|rifled]] [[gun barrel]]. The freebore is located just forward of the |
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==Location and dimensions== |
==Location and dimensions== |
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The chamber is the rearmost portion of a firearm barrel that has been formed to accept a specific cartridge or shell. For firearms having a rifled barrel, the bullet typically extends forward from the leading edge of the cartridge. 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 comprised of both a '''freebore''' and a '''leade.''' The freebore is typically slightly larger in diameter than the rifling grooves in order to allow the cartridge to be loaded into the chamber without the resistance. The leade is the tapered section of the throat that transitions in diameter from the freebore to the rifling lands at a small angle, typically between 1 and 3 degrees. |
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The chamber is the rearmost portion of a rifled barrel enlarged to hold a cartridge containing a bullet. The bullet typically extends forward from the leading edge of the cartridge. The portion of the barrel forward of the chamber tapers into the rifling as a '''throat'''. Each barrel is manufactured with a section of grove diameter (or larger) freebore to allow the cartridge to be loaded into the chamber without the resistance encountered if the bullet were forced into the rifling. Freebore diameter in excess of groove diameter for easy loading allows potential bullet misalignment. Increasing freebore length permits bullets to extend further out of the cartridge case to increase space for propellant within the case.<ref>{{cite web |url=https://loaddata.com/Article/BenchTopics/OAL-and-Free-Bore/125 |title=OAL and Free-Bore |last=Mann |first=Richard |website= |publisher=Wolfe Publishing Company |accessdate=21 June 2018 }}</ref> Rifling lands taper from groove diameter to land diameter in a '''leade''' forward of the freebore.<ref>{{cite web |url=http://bisonballistics.com/articles/an-introduction-to-rifle-chambers |title=An Introduction to Rifle Chambers |last=Cali |first=Damon |website= |publisher=Bison Ballistics |accessdate=21 June 2018 }}</ref> Increasing freebore length delays the onset of resistance from friction and deformation as the bullet engages rifling, and separates that resistance from the [[internal ballistics]] transition from [[static friction]] to sliding friction. Dimensions of freebore length and diameter may gradually increase if hot powder gas melts the interior barrel surface when the rifle is fired. |
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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.<ref>{{cite web |url=https://loaddata.com/Article/BenchTopics/OAL-and-Free-Bore/125 |title=OAL and Free-Bore |last=Mann |first=Richard |website= |publisher=Wolfe Publishing Company |accessdate=21 June 2018 }}</ref> 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. |
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==Sources== |
==Sources== |
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Revision as of 19:47, 18 August 2019
In firearms, freebore (also free-bore or free bore) is the forward most portion of the chamber of a rifled gun barrel. The freebore is located just forward of the chamber neck and is usually cylindrical in shape. The diameter of the freebore is always larger than the groove diameter of the gun barrel bore so that no rifling is present and projectiles used in the firearm can move in the freebore without resistance.[1]
Location and dimensions
The chamber is the rearmost portion of a firearm barrel that has been formed to accept a specific cartridge or shell. For firearms having a rifled barrel, the bullet typically extends forward from the leading edge of the cartridge. 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 comprised of both a freebore and a leade. The freebore is typically slightly larger in diameter than the rifling grooves in order to allow the cartridge to be loaded into the chamber without the resistance. The leade is the tapered section of the throat that transitions in diameter from the freebore to the rifling lands at a small 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.[2] 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
- ^ "Glossary – SAAMI". Retrieved 2019-05-05.
- ^ Mann, Richard. "OAL and Free-Bore". Wolfe Publishing Company. Retrieved 21 June 2018.