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

Polygonal rifling is a type of rifling wherein the traditional lands and grooves are replaced instead by "hills and valleys" in a rounded polygonal pattern, usually a hexagon. Image File history File links Polygonal_vs_normal_rifling. ... Image File history File links Polygonal_vs_normal_rifling. ... Rifling of a Canon de 75 modèle 1897 A 35 caliber Remington, with a microgrove rifled barrel with a right hand twist. ... Look up polygon in Wiktionary, the free dictionary. ...

History

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 last common rifle to use polygonal rifling was the Lee-Metford rifle, named after the Metford rifling, a 7 sided polygonal type rifling. The switch to cordite from black powder proved too much for the shallow rifling in the relatively soft barrels of the time, and the Lee-Metford became the Lee-Enfield when the Metford rifling was dropped. Heckler & Koch was the first manufacturer to begin using polygonal rifling in modern arms. Companies that utilize this method today include Heckler & Koch, Glock and Kahr arms. Polygonal rifling is usually only found in pistol barrels, and is less common in rifles, However some high end rifles like the PSG-1 or the MSG-90 use polygonal bores. Cordite is a particular family of smokeless propellants made by combining two high explosives: nitrocellulose and nitroglycerin, i. ... The Lee-Metford rifle was a breech-loading British army service rifle, combining James Paris Lees rear-locking bolt system and ten-round magazine with a seven groove rifled barrel designed by William Ellis Metford. ... Cordite is a particular family of smokeless propellants made by combining two high explosives: nitrocellulose and nitroglycerin, i. ... Black powder for sporting can be freely bought in Switzerland. ... Heckler & Koch G41 Heckler & Koch GmbH (H&K) (pronounced //) is a German weapons manufacturing company famous for various series of small firearms, notably the MP5 submachine gun, the MP7 personal defense weapon, USP series handguns, high-precision PSG1 sniper rifle, and the G3 and G36 assault rifles. ... Heckler & Koch G41 Heckler & Koch GmbH (H&K) (pronounced //) is a German weapons manufacturing company famous for various series of small firearms, notably the MP5 submachine gun, the MP7 personal defense weapon, USP series handguns, high-precision PSG1 sniper rifle, and the G3 and G36 assault rifles. ... Glock is an Austrian defense contractor (named after the founder Gaston Glock) founded in 1963 in Deutsch-Wagram, near Vienna, Austria. ... A Browning 9 millimeter Hi-Power Ordnance pistol of the French Navy, 19th century, using a Percussion cap mechanism Derringers were small and easily hidden. ... A rifle is a firearm with a stock and a barrel that has a spiral groove or grooves (rifling) cut into its interior. ... Heckler und Koch PSG-1 sniper rifle The PSG-1 is a widely known semi-automatic sniper rifle designed by the German company Heckler und Koch. ...

It should be noted that the term "polygonal rifling" is fairly general, and different manufacturers employ varying polygonal rifling profiles.

Advantages

A number of advantages are claimed by the supporters of polygonal rifling. These include:

• Higher velocities due to reduced friction of the bullet in the barrel, as the polygonal rifling has less surface area than the lands and grooves of a traditionally rifled barrel
• Less bullet deformation, resulting in reduced drag on the bullet which helps to increase range and accuracy
• Increased barrel life and reduced buildup of copper or lead within the barrel

However, it should be noted that precision target pistols, such as those used in bullseye and IHMSA, almost universally use traditional rifling, as do target rifles. The debate among target shooters is almost always one of cut vs. button rifled barrels, as traditional rifling is dominant. The areas where polygonal rifled barrels are used competitively is in pistol action shooting, such as IDPA and IPSC competitions. Bullseye, also known as Conventional Pistol, is a sport in which participants shoot handguns at paper targets at fixed distances and time limits. ... Metallic silhouette shooting is a group of target shooting disciplines that involves shooting at metal cutouts representing game animals at varying distances. ... Rifling of a Canon de 75 modèle 1897 A 35 caliber Remington, with a microgrove rifled barrel with a right hand twist. ... Action shooting is a term that encompasses target shooting events where the shooters score is based on both the accuracy and elapsed time. ... The International Defensive Pistol Association promotes defensive pistol shooting as a sport, using equipment including full-charge service ammunition to solve simulated real world self-defense scenarios. ... IPSC can mean: International Practical Shooting Confederation Inhibitory Post-Synaptic Current, in neurobiology iPSC, any of several high-performance computers manufactured by Intel This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

Part of the difference may be that most polygonal rifling is produced by hammer forging the barrel around a mandrel containing a reverse impression of the rifling. Hammer forging machines are tremendously expensive, far out of the reach of custom gunsmiths (unless they buy pre-rifled blanks), and so are generally only used for production barrels by large companies. The main advantage of a hammer forging process is that it can take a bored barrel blank and rifle, chamber, and contour it on one step. Invented in Germany in 1939, hammer forging has remained popular in Europe, but was only later used by gunmakers in the United States. The hammer forging process produces large amounts of stress in the barrel that must be relieved by careful 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 tend to avoid hammer forged barrels, and thus limits them in the type of available rifling. A blacksmiths forge For finery forges (making iron) see finery forge. ... 1939 (MCMXXXIX) was a common year starting on Sunday (link will take you to calendar). ... World map showing Europe A satellite composite image of Europe Europe is one of the seven traditional continents of the Earth. ...

Lead bullets and polygonal rifling

The manufacturer Glock advises against using lead bullets (meaning bullets not covered by a copper jacket) in their polygonally rifled barrels, which has lead to a widespread belief that polygonal rifling is not compatible with lead bullets. Noted firearms expert Gale McMillan has also commented that lead bullets and polygonal rifling are not a good mix. However, since neither H&K nor Kahr recommend against lead bullets in their polygonal rifled barrels, it is probable that there is an additional factor involved in Glock's warning. One explanation is that Glock barrels have a fairly sharp transition between the chamber and the rifling, and this area is prone to lead buildup if lead bullets are used. This buildup may result in failures to fully return to battery, allowing the gun to fire with the case not fully supported by the chamber, leading to a potentially dangerous case failure. The other explanation is that Glock's barrels may be more prone than normal to leading, which is the buildup of lead in the bore that happens in nearly all firearms firing high velocity lead bullets. This lead buildup must be cleaned out regularly, or the barrel can become constricted and result in higher than normal pressures.

See also

• Ballistic fingerprinting

Ballistic fingerprinting, a sub-category of firearms examination, is a forensic method that is intended help to find the gun that was used in a crime by matching the bullets striations (or striae) with the rifled barrel through which it was fired, or by matching marks on the cartridge...

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.