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Polygonal rifling
- Thread starter bradtothebone
- Start date
Polygonal Rifling
Polygonal rifling is supposed to give slightly higher velocities than traditional rifling (ie: cut, buttoned, or hammer forged) because it causes less deformation of the bullet jacket and therefore yields a tighter gas seal. It is also supposed to foul less due to the decreased jacket deformation and be less susceptible to ablation (gas 'cutting', especially in the throat area) due to better heat resistance because there are no sharp bearing surfaces like those found along the leading edges of the lands of the more traditional rifling. This is the theoretical answer and is the one proposed by HK, as they use it on several of their rifles and handguns. Incidentally, HK also says that bullets of .45 calibre are the ideal caliber to benefit from the supposed advantages of polygonal rifling, but they do not say why or provide any insight into how they derived this information.
I have a .308 WIN with a 19.5 " polygonal bore (an HK) and another .308 bolt gun with a 24" Pac-Nor barrel with traditional rifling. Pac-Nor makes great barrels and I can personally vouch for them. They are as good as any other first class barrel makers barrels. As far as the benefits of polygonal rifling go, it is my opinion that it works as good as cut or buttoned or hammered barrels but I haven't found it to work any better either. The Pac-Nor shoots the same load a little faster, but because of the difference in barrel lengths, any velocity comparisons are moot. Just my two cents worth...hope it helps.
Jim
Polygonal rifling is supposed to give slightly higher velocities than traditional rifling (ie: cut, buttoned, or hammer forged) because it causes less deformation of the bullet jacket and therefore yields a tighter gas seal. It is also supposed to foul less due to the decreased jacket deformation and be less susceptible to ablation (gas 'cutting', especially in the throat area) due to better heat resistance because there are no sharp bearing surfaces like those found along the leading edges of the lands of the more traditional rifling. This is the theoretical answer and is the one proposed by HK, as they use it on several of their rifles and handguns. Incidentally, HK also says that bullets of .45 calibre are the ideal caliber to benefit from the supposed advantages of polygonal rifling, but they do not say why or provide any insight into how they derived this information.
I have a .308 WIN with a 19.5 " polygonal bore (an HK) and another .308 bolt gun with a 24" Pac-Nor barrel with traditional rifling. Pac-Nor makes great barrels and I can personally vouch for them. They are as good as any other first class barrel makers barrels. As far as the benefits of polygonal rifling go, it is my opinion that it works as good as cut or buttoned or hammered barrels but I haven't found it to work any better either. The Pac-Nor shoots the same load a little faster, but because of the difference in barrel lengths, any velocity comparisons are moot. Just my two cents worth...hope it helps.
Jim
Lothar Walther offers polygonal rifling in some of their barrels. They claim that they lose about 5% accurracy to a standard match rifling system.
Most often used in high volume firing applications such as full auto rifles or magnum rifle chamberings where large amounts of powder are being burned.
Not having any sharp corners they do not tend to pick up fouling as quick as a standard rifling profile and will run longer between cleaning maintenance requirements.Without any sharp edges they will last longer before showing throat erosion also. A sharp edge will always burn off before a rounded curve.
The 5R rifling used in the Rock Arsenal barrels is kind of a half poly and half standard form of rifling. It has one sharp corner on the lands and one 5 degree sloped shoulder . The polygonal concept works well and is excellant on a duty rifle but for absolute best accuracy its hard to beat the standard rifling profiles done by any of the accepted rifling methods.
Most often used in high volume firing applications such as full auto rifles or magnum rifle chamberings where large amounts of powder are being burned.
Not having any sharp corners they do not tend to pick up fouling as quick as a standard rifling profile and will run longer between cleaning maintenance requirements.Without any sharp edges they will last longer before showing throat erosion also. A sharp edge will always burn off before a rounded curve.
The 5R rifling used in the Rock Arsenal barrels is kind of a half poly and half standard form of rifling. It has one sharp corner on the lands and one 5 degree sloped shoulder . The polygonal concept works well and is excellant on a duty rifle but for absolute best accuracy its hard to beat the standard rifling profiles done by any of the accepted rifling methods.
