Polygon rifling

[GaryD]

I am looking MOA rifles for a new long range shooter and they use a polygon barrel. I got to thinking about what effects the rifling may have on bullet after it leaves the barrel. In my mind I see an octagon shaped bullet spinning through the air with flat sides.

1. Would it have a lower bc compaired to same bullet fired from standard land and groove barrel due to a possible increase drag from turbalance around the flat sides on the bullet?

2. Would there be an increase of spin drift with the flat sides "paddling" the air?

3. Would it be more stable going through transonic speed due to ? ( dimples in a golf ball) effect

Or am I just over thinking it and need to just go buy one and have fun

Gary

 

[JPeelen]

If you look at the rifling marks which a traditional land/groove barrel leaves on the bullet, one would expect that the turbulence they cause is larger than by the smooth surface created by a polygon profile.

Polygon barrels are cold hammer forged, and a such have more residual internal stress than barrels that are cut. I personally love polygon barrels since my military service, because cleaning them was much, much easier than conventionally profiled machine gun barrels.
Polygon barrels last "forever" and in my experience (P9S pistol, and SL6 as well as SL7 rifles for nearly three decades) shoot extremely well. But for top notch accuracy (0.5 MOA and below) I would choose a traditionally cut barrel.

 

[JRS]

If you look at the rifling marks which a traditional land/groove barrel leaves on the bullet, one would expect that the turbulence they cause is larger than by the smooth surface created by a polygon profile.

Polygon barrels are cold hammer forged, and a such have more residual internal stress than barrels that are cut. I personally love polygon barrels since my military service, because cleaning them was much, much easier than conventionally profiled machine gun barrels.
Polygon barrels last "forever" and in my experience (P9S pistol, and SL6 as well as SL7 rifles for nearly three decades) shoot extremely well. But for top notch accuracy (0.5 MOA and below) I would choose a traditionally cut barrel.

You might want to rethink that one. Gary Schneider's barrels are NOT cold hammer forged, and are used by many top guns the world over

 

[JPeelen]

Thanks for the correction. I was not aware of that.

 

[Bryan Litz Ballistics]

I don't think there would be much difference in the bullets flight, at least out thru it's supersonic range.

Polygonal riflings don't put 'flats' on a bullet like a hex nut, the grooves are just more rounded than square.

The biggest effect I've measured from different riflings is how well they allow the bullet to retain RPM's as the bullet flies. This is important when the bullet slows to transonic speed at long range and stability becomes a factor. The more RPM's the bullet retains, the better shape it will be in. Furthermore, the nature of the riflings and the surface finish of the bearing surface have an effect on some of the aerodynamics (Magnus and pitch damping derivatives, basically viscous effects arising from the boundary layer) that partially determine the bullets transonic stability.

So short answer, I don't think you'll see a difference out to whatever range your bullet stays above about 1340 fps, which is beyond most hunting ranges anyways, since hunting bullets typically need ~1800 fps for reliable expansion (more or less depending on design, etc).

-Bryan

 

[dcali]

There's an old military research paper floating around the web that attempted to measure the effect of rifling on aerodynamics. Long story short, they found that there was a small but basically negligible impact on some aerodynamic coefficients - and that was the difference between rifled and unrifled bullets. It stands to reason that the difference between different types of rifling would be smaller still.

 

[mikecr]

Schneider & Pacnor barrels are no more polygon than any other radiused rifling out there. More like wore out buttons..
Anyway, they don't apply to the question at hand.

 

[GaryD]

Thanks all. From everyone's response the effect would be smaller than my shooting ability. I just received Bryan's books and have started diving into them.

Gary