Polygonal Rifling Difference

Glock uses two different types of polygonal rifling, as illustrated above...The circle in the middle represents a bullet, and the yellow represents the gap bewteen the bullet and the barrel.

Glock uses the octogonal rifling on the 45 caliber to provide a better gas seal...and uses the hexagonal on all other calibers..to my knowledge.

Land and groove rifling has a cross-section more similar to the following picture.



A for the topic of lead....Unjacketed lead bullets have a tendency to "smear" lead into the voids represented by the yellow color in the first picture. This will cause the barrel pressure to rise dramatically in as little as 100 rounds or less. This could mean a Kb....and/or possibly a lodged bullet. However, the land and groove rifling does not have this problem, and unjacketed lead can be safely fired.

The resoning behind polygonal rifling is that even with the gaps shown in yellow, there is significantly less pressure leakage that when using conventionally rifled "land and groove" barrels....This will prodice a higher muzzle velocity in a shorter barrel than is normally acheivable with land and groove rifling...with one drawback...you cant use lead bullets....

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arinvolvo

Good ANSWER! Good ANSWER!

The resoning behind polygonal rifling is that even with the gaps shown in yellow, there is significantly less pressure leakage that when using conventionally rifled "land and groove" barrels....This will prodice a higher muzzle velocity in a shorter barrel than is normally acheivable with land and groove rifling...with one drawback...you cant use lead bullets....

Click to expand...

With lead bullets, you don't need to worry as properly sized lead bullets should do a pretty good job of sealing. What they are basically doing is making the barrel better for copper jacket and worse for lead...from what I can tell.

And here's a question, what about other manufacturers? For example, my wife want a Kahr.. from what I've heard you can shoot lead through the poly rifling of a Kahr...

Glock rifling, while mostly polygonal, is different that Kahr, HK, Steyr, IMI and Stahl polygonal bores. Glock has no lands, but it does have corners, rather than the smooth transitions between polygon sides in other designs. It looks more aggressive, and likely is.

The Glock problem gave all poly barrels a bad name, but I've never really heard reports of leaded up poly barrels before the US introduction of the Glock. Make you go "hmmm".

As someone will likely point out, the harder the lead, the less likely the leading. Hard cast bullets have been safely used in standard Glock barrels.

Whatever you're shooting, it pays to look for signs of leading when using cast bullets. My brother's .22 pistol once leaded up. Go figure.

My Glock does not have polygonal rifling.

It is certainly NOT as shown in arinvolvo's excellent diagram.
As Handy points out, it's closer to conventional rifling that's been washed out some. It isn't exactly conventional, but it's sure not polygonal in profile either, despite what their website claims. By the way, Glock says their barrels are "polygonal", except for the 45, which is "octagonal". Never mind that an octagon is a polygon.

I have a H&K USP; it is polygonal, just like the picture in arinvolvo's diagram. I can't get it to scan, though.

One correction to arinvolvo's diagram. The bullet diameter fits the outside point dimension of the polygon, not the inside flats. There are no gaps between the bullet diameter and the (for lack of a better term) grooves. There is no blow by (with proper diameter bullets).

The H&K owner's manual has no warning about lead bullets. Just the usual crap about reloads voiding the warranty.

Good answers thus far....Polygonal barrels DO come in many flavors / styles. The Kahr guns have nicely rounded style "lands and grooves" in there polygonal barrels.......nice to clean and supposed to catch all of the pressure...shorter barrels benefit from this...more push=more fps.
My CZ83 Mak 9x18 has almost NO ANYTHING for deviations from a perfectly round barrel....but has the same/better great accuracy that my .380/land and grooves 83 did....the barrel looks damn near "round" even when using a good bore light....
Shoot well

Fellas'

I don't know about Glorks, but I've been shooting copper-washed lead through my H&K for years. Mostly Ranier's or Berry's 180 gr driven with Blue Dot to 950 - 1000 fps. Never had a problem with shooting or cleaning. As cheaply as you can buy these, why cast?

Of course, that incestuous product of miscegnation between the German Legos company & the Austrian military may have it's own set of problems. But I'll leave that subject alone. Snrk! 900F

There are a variety of reason for casting, cheaper for one (mostly free lead), and you can size (or not) to the best size for your particular barrel.

And I get good hardcast lead cheaper than Ranier or Berry's ($18 for 500 .38 LRN's)

Muck like this, IMO.

By the way, Glock says their barrels are "polygonal", except for the 45, which is "octagonal". Never mind that an octagon is a polygon.

Click to expand...

My Glock manual says hexagonal rifling except for the octagonal rifling for the .45s...

hksw....that pic is probably a much better representation of the polygonal rifling on the glock.