Home Forums Hunting & Shooting Ask The Gunwriters Ken, could you explain polygonal rifling...

From what I understand, it is supposed to be a good thing. HK boasts that it gives better accuracy and velocity in their USP pistols for example, but I am a little fuzzy on what it means. And is it really all it is cut out to be?

Polygonal rifling has neither lands nor grooves. Look at any hex (hexagonal, six-sided) nut, ignore the threaded hole, and you have in your hand an approximate solid model of the hole (bore) in a cross-section of a Whitworth barrel from about 1860 AD. The "corners" of the Whitworth rifling were rounded, not sharp like the corners of the nut. Otherwise, the nut'll give you an idea of what six-sided polygonal rifling looked like -- six straight sides, six arcs connecting them.

I have no idea how much easier or harder it is to rifle a barrel this way -- or how much better or worse than land-and-groove rifling this kind of rifling may be. It obviously deforms round bullets and produces UNround projectiles -- whether they fly with more or less air turbulence around them, I can't guess and certainly don't know. I assume that if this kind of rifling were in major ways superior to land-and-groove rifling, it'd be the norm in custom barrels at least, if not in production barrels. My guess is that its main attraction lies in its novelty.

Polygonal rifling may be very usefull in muzzleloaders if the projectile is also polygonal shaped thus allowing very hard lead or other materials to be utlized as projectiles. There will be no gruve cutting in the the projectile as there is with rifled barrels. The potentional for higher velocities exists as friction can in theory be reduced,
the bullet will ride on the edges of the flats as it is twisted down the bore, again no cutting of gruves in bullet. the advantage of this may be minimized in flight as the rotation of the bullet has possibly greator air resistance due to the flat portions. air flows over smooth round surfaces with less drag than non round surfaces.
secondly reloading into a cartrige would be difficult with out hexagonal or like shaped cases. Then there is the distribution of pressure in the case when fired. Pressue will tend to spike in the corners as it will not "flow" around the case equeally as in a tubelar case.
Polygonal bullets have proven to be very accurate from Whitworth muzzleloaders. the bullets tend to be of smaller caliber, 45, than the muskets of the day they did have similar weights due to their long design, thus they flew better. Today we look to sectional density to see how a long bullet is superior at longer distance.
I have a desire to own a Whitworth rife just for these very reasons.

Bullwnkl.

A couple of issues back in Rifle, Seyfried put an original Whitworth through the paces and shows some excellent photos of the muzzle and bullets used. He found little to no difference between using conical or hexagonal shaped bullets. He did state that it put a hexagonal hole in the hide of the cow elk he shot with it. It's an interesting read.