H&K barrel rifling

[4thHorseman]

My H&K USP compact 40 barrel rifling looks unusual in the sense I have never seen any thing like it before. It swirls as if it comes to a point. Not at all simialiar to other manufactures.
Any reason to manufacture it this way, any advantage ot disadvantage?
Any ideas or comments, guys?
Thx

 

[SDC]

It's "polygonal" rifling, the same as on Glock pistols; there are some advantages (primarily less friction and bullt deformation), but there's also a disadvantage, in that firing soft lead bullets will usually leave substantial leading in the bore, and firing jacketed ammo afterwards without cleaning the barrel jacks up pressures.

 

[Tactical]

It makes for very easy cleaning. Unlike a land and groove barrel, the polygonal barrel keeps gas pressure from slipping from behind the bullet through the grooves which increases velocity of the bullet.

 

[Standing Wolf]

It swirls as if it comes to a point.

I'm not entirely sure what you mean, nor am I even remotely familiar with H & K pistols, but I've heard some pistols have rifling whose rate of twist increases toward the muzzle.

 

[SDC]

Here's a web page that's got some phots showing the difference between conventional and polygonal rifling: http://www.firearmsid.com/A_bulletIDrifling.htm ; what SW is thinking of is called "gain twist" where a bore starts out rifled at one rate (say 1:12) and the rate of twist speeds up (to, for example, 1:8).

 

[Archie]

Polygonal rifling

The cross section of the barrel shows the perimeter of the interior to be composed of a number of "sides", all straight and equal in length, connected by equal angles. There are no curves to be found.
H&K uses polygonal rifling in the USP series. At one time, H&K rifled all their guns, pistols, rifles and sub-machine guns polygonally. I've heard the long guns are now conventionally rifled, but I haven't looked at any for a long time, so I don't really know.

My USP 40 is polygonally rifled. Shooting lead through it does not cause a problem. It leads some, but no more than conventionally rifled pistols I own (several and varied) and is much easier to clean.

A polygon is defined as "...a closed plane figure bounded by straight sides."

The Glock 17 I have does not have polygonal rifling. I don't know how to describe it, other than it looks like conventional rifling with the edges of the lands melted. It looks much like the style shown in the website referenced above (firearmsid). Glock calls it polygonal, but it is not a polygon like they showed me in geometry.
The manual that came with my Glock doesn't say anything about lead bullets, but it says something about not shooting reloads. I rather think that's more of a lawyer language thing than a practical consideration.

I find it amusing: The Glock website used to advertise their pistols has having "polygonal" rifling, except for the 45 ACP version that was rifled "octagonally". That's a little odd, as an octagon is an eight sided polygon, and a polygon is undeterminate, having "many" sides. I suppose this is one of those cases of advertising being written by someone other than one knowledgable in the field. (Like a copywriter rather than someone schooled in geometry.)
They've changed the copy now to read "hexagonal" for most and "octagonal" for the 45's. As I look at my G 17, it has six lands and grooves... at least they can count. And I must admit, whatever style or name one puts on it, it does stabilize the bullets and shoots pretty well.

Polygonal rifling is supposed to provide a tighter gas seal, less friction and therefore greater velocity. Probably better accuracy and lowers cholesterol, too.

It does work properly. It's easy to clean (and determine to be clean). Anything more than that is marketing hype.

 

[clubsoda22]

My USP .40 did not have polygonal rifling from the factory. The first runs of USP's in 1993 had conventional rifling.

 

[vikesh]

great link SDC

learnt something today

 

[mete]

The P7 M10 also has conventional rifling. Polygonal rifling has been made in 6, 8, and 10 sided versions. The cross section for the hex is a hexagon with rounded corners. Thiugh it's not a true polygon , what else would you call it ?