Weren't there some WW1 artillery pieces that were hex barrelled??

The main advantage is that in small arms they are easier to clean as there are not any angles in which the debris and fouling can easily collect. For accuracy traditional riflings still rule the roost.

Thanks for the reply wagner. Do you have any personal experience with this rifling? The ease of cleaning issue makes sense. I have talked to a few rifle traget shooters I know and they claim better accuracy due to the rifling not putting grooves in the bullet and they believe that heat distortion is less. The theory is that less heat goes into the barrel because there are no sharp corners to pick up heat from the burning propellant. Also they say the barrels last longer because again there are no concentrated hot spots like there is at the corners of conventional rifling. Therefore less wear at in the beginning of the rifling where it usually is worse. All these claims led me to conclude that similar advantages might be had in cannons. I know that barrel wear is a big issue in big guns. Anything that would lessen wear would be good I would think. Any comments?

I know that H&K uses polygonal rifling, there web site is under construction but I found the "unofficial" home site at According the their FAQ sheet "The advantages of polygonal rifling are that it gives a better gas seal with less bullet deformation resulting in slightly higher muzzle velocity, slightly better accuracy, easier cleaning characteristics, and a prolonged barrel life". Not sure if we can believe marketing hype but there it is.

One note is that hexagonal shaped bores are easier to manufacture (from a technological view), which is why many early rifles had hex bores.

Many modern rifles use hammer forged barrels. Rifling pattern doesn't make much difference to the forging machine, one pattern is about as easy as another. By the time the hot gases get to the riflings the bullet is already past, too late to make any difference. If there was any accuracy advantage hexagonal riflings would be used by competitive shooters; they aren't. Neither does military artillery. The shallow angles engaging the bullet will not provide as good a grip so the bullet has more chance to skid or slip when first accelerating. If one carries the principle to the extreme one ends up with the 'Lancaster' style rifling in which the bore is an oval, essentially a two groove design with no shoulders.

wagner, Most of your thoughts on this make sense except the one about heat. My experience is that the worst barrel errosion occurs at the beginning of rifling and it is caused by hot high velocity gas going past the rifling at that point. The heat effect is more intense on any exposed sharp edges and the more turbulent the flow the more heat transfer. So I think barrel wear in that area should be better. I am puzzled but agree with your statement that competitive shooters do not seem to favor polygonal rifling. I have read a few test reviews where they have made the claim for better accuracy in target rifles but it doesn't seem to be something shooters clamor for. I'm going to check with a couple of competition marksman that I know to see what they say. A also seem to see more pistols made this way than rifles. Wonder why?

Basically erosion of the throat is apt to effect ballistics such as velocity more than accuracy. Velocities will decrease but the remaining riflings will still stabilize the projectile. Modern naval guns, AA guns, and field artillery often incorporate velocity measuring systems capable of compensating for velocity variations on a shot by shot basis, even at high rates of fire. If the gun loses a few fps velocity with every couple of shots the fire control automatically compensates. The general rule in shooting is that the last few inches of the barrel [the muzzle] are more important to accuracy than the first few inches just as the base of the projectile is more important than the nose.