Polygonal Rifling - History

History

Left image: 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.
Right image: Hexagonal rifling of Le Pétulant (detail).

While polygonal rifling has been around since the earliest days of rifled barrels, it had faded out of use by the time of the early cordite cartridges.

The principle of the polygonal barrel was proposed in 1853 by Sir Joseph Whitworth, a prominent British engineer and entrepreneur. Whitworth experimented with cannons using twisted hexagonal barrels instead of traditional round rifled barrels, which was patented in 1854. In 1856, this concept was demonstrated in a series of experiments using brass howitzers. The British military however rejected Whitworths polygonal rifled designs. Whitworth believed that polygonal rifling could be used to create a more accurate rifled musket to replace the Pattern 1853 Enfield. During the American Civil War Whitworths polygonal rifled Whitworth rifle was successfully used by the Confederate States Army Whitworth Sharpshooters. The Whitworth rifle is often called the 'sharpshooter' because of its accuracy compared to other rifled muskets of its era and is considered one of the earliest examples of a sniper rifle. The last common rifle to use polygonal rifling was the Lee-Metford rifle, named after the Metford rifling, and the Arisaka rifles designed by Col. Arisaka. The switch to cordite from black powder proved too much for the shallow rifling in the relatively soft barrels of the Metford, and the Lee-Metford became the Lee-Enfield when the Metford rifling was dropped, however, Arisakas were manufactured until the surrender of the Imperial Japanese Army in 1945, it has been proven that Arisaka rifling was more durable, and the accuracy of many captured rifles can attest to this.

During World War 2 polygonal rifling emerged again in the German MG 42 machine gun. It was an outgrowth of a cold-hammer forging process developed by German engineers prior to World War 2. The process addressed the need to produce more durable machine gun barrels in less time than those produced with traditional methods. The MG42 successor the Rheinmetall MG 3 machine gun can also have polygonal rifling. Heckler & Koch was the first manufacturer to begin using polygonal rifling in modern small arms like the G3A3 assault rifle and several semi automatic hunting rifles like the HK SL7.

Companies that utilize this method today include Tanfoglio, Heckler & Koch, Glock, Magnum Research, Česká Zbrojovka and Kahr Arms. Polygonal rifling is usually found only in pistol barrels, and is less common in rifles, however some extremely high end rifles like the Heckler & Koch PSG1 and LaRue Tactical Stealth System sniper rifle use polygonal bores.

The term "polygonal rifling" is fairly general, and different manufacturers employ varying polygonal rifling profiles. H&K, CZ and Glock use a female type of polygonal rifling similar to the bore shown above right. 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 (Pac Nor) and LWRC use a rifling more like the conventional rifling with both of the lands sides being sloped but has a flat top and defined corners, this type of rifling is more of a canted land type of rifling than polygonal rifling.