Polygonal rifling

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Conventional eight groove rifling on the left, and octagonal polygonal rifling on the right

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

Glock pistols, octagonal rifling is used in the large diameter .45 ACP bore, which has an 11.23 mm (0.442 in) diameter, since it resembles a circle more closely than the hexagonal rifling used in smaller diameter bores.[1]

History

Rifled mountain cannon of the French La Hitte system, "Canon de montagne de 4 modèle 1859 Le Pétulant". Caliber: 86 mm. Length: 0.82 m. Weight: 101 kg (208 kg with carriage). Ammunition: 4 kg shell. Its hexagonal rifling is shown in detail.

The principle of the polygonal barrel was proposed in 1853 by Sir

small arms, believing that polygonal rifling could be used to create a more accurate rifled musket to replace the Pattern 1853 Enfield
.

During the

breechloading Sharps rifle used by the Union Army) and is considered one of the earliest examples of a sniper rifle. The Whitworth sharpshooters killed multiple high-ranking Union officers, most famously Major General John Sedgwick, who was fatally shot at a range of 1,000 yards (910 m) during the Battle of Spotsylvania Court House
.

The last

6 mm Lee Navy was analogous to Cordite. However, the Arisakas were manufactured extensively for the Imperial Japanese Army
from 1897 to 1945 with no excessive rifling erosion problems, as the Japanese had adopted a better, non-erosive, rifle powder.

During

Rheinmetall MG 3
machine gun, can also have polygonal rifling.

high end precision rifles like the Heckler & Koch PSG1 and its Pakistani variant PSR-90
, and the LaRue Tactical Stealth System sniper rifle use polygonal bores.

Design

Hexagonal polygonal rifling.

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

IDPA and IPSC
competitions.

Part of the difference may be that most polygonal rifling is produced by hammer

heat treatment, a process that is less necessary in a traditionally cut or button rifled barrel. Due to the potential for residual stress
causing accuracy problems, precision shooters in the United States tend to avoid hammer forged barrels, and this limits them in the type of available rifling. From a practical standpoint, any accuracy issues resulting from the residual stresses of hammer forging are extremely unlikely to be an issue in a defense or service pistol, or a typical hunting rifle.

Variations

The FX-05 Xiuhcoatl is an example of an assault rifle that uses polygonal rifling.

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 "

FBI GRC file, the land and groove widths for these firearms are listed as 0.000. However, forensic identification of firearms (in court-cases, etc.) is based on microscopic examination of tooling marks on the surface of the bore, produced by the manufacturing process and modified by the drag of bullet jackets on that same surface. Thus, the bore surface of individual firearms is always unique.[5]

See also

References

  1. ^ a b Barrel History Archived 2010-04-20 at the Wayback Machine
  2. ^ Barrels and Bullets: Conventional Versus Polygonal Rifling by Dennis Cantrell 06/08/2010
  3. ^ SL7 Polygonlauf, Vielflächenlauf by Lutz Möller (German)
  4. ^ Peter Alan Kasler - Glock: The New Wave in Combat Handguns, p. 138
  5. ^ "National Institute of Justice Firearm Examiner Training".

External links