Polygonal rifling
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Polygonal rifling (/pəˈlɪɡənəl/ pə-LIG-ə-nəl) is a type of gun barrel rifling where the traditional sharp-edged "lands and grooves" are replaced by less pronounced "hills and valleys", so the barrel bore has a polygonal (usually hexagonal or octagonal) cross-sectional profile.
Polygonal riflings with a larger number of edges have shallower corners, which provide a better gas
History
The principle of the polygonal barrel was proposed in 1853 by Sir
During the
The last
During
Design
A number of advantages are claimed by the supporters of polygonal rifling. These include:
- Not compromising the barrel's thickness in the area of each groove as with traditional rifling, and also less sensitive to stress concentration-induced barrel failure.
- Providing a better gas seal around the projectile as polygonal bores tend to have shallower, smoother edges with a slightly smaller bore area, which translates into more efficient seal of the combustion gases trapped behind the bullet,[4] slightly greater (consistency in) muzzle velocities and slightly increased accuracy.[1]
- Less bullet deformation, resulting in less frictional resistance when the bullet travels through the barrel, which helps to increase muzzle velocity. The lack of sharp surface deformation on the bullet (rifling marks) also reduces drag in flight.
- Reduced buildup of copper or lead within the barrel, as there are no sharp rifling edges to "shred" into the bullet surface and no pronounced corners that can accumulate foulings difficult to clean, which results in easier maintenance. The reduced fouling also theoretically translates to a simpler "copper equilibrium" profile, which is potentially beneficial to accuracy.
- Prolonged barrel life, as the thermomechanical stress upon the riflings are spread over a larger area, hence less wear over time.
However, precision target pistols such as those used in
Part of the difference may be that most polygonal rifling is produced by hammer
Variations
Different manufacturers employ varying polygonal rifling profiles. H&K, CZ and Glock use a female type of polygonal rifling. This type has a smaller bore area than the male type of polygonal rifling designed and used by Lothar Walther. Other companies such as Noveske Rifleworks (Pac Nor) and LWRC use a rifling more like the conventional rifling, with both of each land's sides being sloped but having a flat top and defined corners; this type of rifling is more a canted land type of rifling than polygonal rifling.
Forensic examination
Polygonal rifling prevents the forensic firearms examiner from microscopically measuring the width of land and groove impressions (so-called "
See also
- Ballistic fingerprinting
- Smoothbore
References
- ^ a b Barrel History Archived 2010-04-20 at the Wayback Machine
- ^ Barrels and Bullets: Conventional Versus Polygonal Rifling by Dennis Cantrell 06/08/2010
- ^ SL7 Polygonlauf, Vielflächenlauf by Lutz Möller (German)
- ^ Peter Alan Kasler - Glock: The New Wave in Combat Handguns, p. 138
- ^ "National Institute of Justice Firearm Examiner Training".
External links
- Glockmeister FAQ, with information on lead bullets in Glock firearms.
- The Gun Zone 2001 e-mail questions, with information on cast bullets in Glock and H&K handguns.
- Barrel making FAQ, with information on methods of making and rifling barrels
- 6mmBR barrel FAQ, covers new polygonal profile button rifled barrels
- Polygonal Rifling, A comment from Gale McMillan about lead bullets and polygonal rifling.