Polygonal Rifling

Since the Glock was introduced about twenty five years ago, one of it's selling points was that it had Polygonal Rifling. This is a "special" type of rifling that, according to Wikipedia's description, "... Is a type of rifling wherein the traditional lands and grooves are replaced by "hills and valleys" in a rounded polygonal pattern, usually a hexagon." Theoretically, the advantages of this over traditional rifling are: Less friction since there is less surface area, less bullet deformation which can increase range, reduction in amount of lead and copper fouling, and finally increased barrel life.

Polygonal rifling is nothing new. It has been around almost as long as rifled barrels have been used. It was a time consuming process to form these barrels and "traditional" rifling was much easier to do. By the late 1800's, polygonal rifling was virtually dead. As we all know, everything old is made new again. In the late 1930's, Germany gunmakers started using polygonal rifling, again, and it has slowly been reaccepted in Europe and now the U.S.

Currently, Glock, Kahr, Magnum Research, and HK are the big users of this type of rifling---but only in pistols. Polygonal rifling is extremely rare in long guns and even rarer in target rifles. Apparently, for all it's hype, polygonal rifling is not any better then traditional rifling and possibly worse for long barrel or long range accuracy. It it was more accurate and deformed the bullets less then traditional rifling, this would increase accuracy in long range shooting. This appears not to be the case. In pictures of recovered bullets, the polygonal rifling does cause slight deformation, which looked to me like little valleys grooved in the copper jacket of the bullet. Traditional rifling causes small cuts int he jacket of the bullet. 6 of one, half-dozen of the other. However, Glocks are very popular in pistol shooting circles.

This leads to a major disadvantage to polygonal rifling: Many experts and the Glock company advise that lead bullets (non-jacketed) should not be used in polygonal guns. There have been reports of KABOOMS (insider name for a gun blowing up) with Glocks using lead bullets. I have read reports but never seen actual proof of this. The Glock owners manual and website specifically state not to use lead bullets. Kahr and HK's do not come with this warning. The notion is that lead bullets leave a thin film of lead in the barrel each time the gun is fired. This builds up differently in polygonal rifling then in traditional styles. Eventually, the lead buildup is enough to cause the bullet to slow down and cause extreme pressures within the barrel. This can lead to a catastrophic breakdown of the weapon.

Noted Glock website Glockmeister states ( http://glockmeister.com/faq.shtml ): It is not a good idea to shoot bare lead bullets from your Glock. There are two basic reasons, the first is that the polygonal rifling in a Glock barrel really grips the bullet - this causes lead bullets to leave heavy deposits of lead when the gun is fired - heavy deposits of lead can lead to over-pressure problems - over-pressure problems can lead to nasty things like case failures. The second reason is that where the chamber meets the bore there is a sharp full edge (standard rifling does not have such a pronounced edge). This edge can shave off lead from the bullet and cause a headspace problem (the round will not fully seat) - again, this can lead to things like a case failure. Shoot plated or jacketed bullets only.