Polygonal rifling v land and groove rifling

[Radny97]

I'm sure this has been done before but I'm interested to see input on the pros and cons of the two. I understand that some types of polygonal rifling prohibit lead bullets and I have heard arguments that polygonal is cheaper to manufacture in large numbers but that land and groove is more accurate.
Not sure if any of that is true. Anyone have insight?

[DaleA]

You are most definitely correct about polygonal rifling having been discussed before...here's a couple of threads about it:

http://thefiringline.com/forums/show...ight=polygonal

http://thefiringline.com/forums/show...ight=polygonal

I've never owned a firearm with polygonal rifling. From what I've read they can give you a tiny bit more velocity and might be easier to clean.

The question whether or not they are okay for lead is a debatable point, as you can see in the two threads above.

[gyvel]

For some reason, CZ elected to make the 9x18 CZ 82 with polygonal rifling, but didn't do so in the .32 or .380 CZ 83.

[Nathan]

Poly rifling is not supposed to shoot lead, but i've never heard a good why. It is aldo said to be more accurate and have slightly better velocities.


The lead piece seems unproven since a lot of lead has been down Glock barrels without incident????

The accuracy statement is suspect because if true, benchrest barrels would use it. None use it.

I've seen the better velocities in print, but again without much why info to back it up.

My guess is that poly does give better velocities and is cheaper to make.

[DMK]

For some reason, CZ elected to make the 9x18 CZ 82 with polygonal rifling, but didn't do so in the .32 or .380 CZ 83.

The CZ-82 was produced for military contract. Someone in the Czech govt probably specified it.

It also has a chrome lined barrel, which you don't see in any commercial CZ guns.

[jimbob86]

The lead piece seems unproven since a lot of lead has been down Glock barrels without incident????

I know of at least one incident involving lead bullets and .40 cal Glock pistol going all to pieces.....

[Radny97]

Seems like if polygonal were more accurate you would see the bullseye and bianchi cup competitors using it, since accuracy would be one of their most important factors in selecting a gun. I might be wrong but I don't think polygonal rifling is very common in those shooting disciplines.

[jimbob86]

Seems like if polygonal were more accurate you would see the bullseye and bianchi cup competitors using it, since accuracy would be one of their most important factors in selecting a gun. I might be wrong but I don't think polygonal rifling is very common in those shooting disciplines.

Over time, the market is the ultimate arbiter- marketing may produce fads, and short term flash in the pan products, but if you want to know what something is good for, see who is using it for what, over a period of decades.

By those lights, polygonal rifling is utilized by manufacturers of mass produced polymer pistols, because it is cheaper to make. I've never seen an aftermarket barrel with polygonal rifling made, or even advertised, much less actually purchased, to replace a traditional rifled barrel..... if there were such a thing, and it worked well enough to sell well over a long period of time, I'm sure I would have heard about it......... so I believe that if what all the Glock fan-boys say were true about polygonal rifling, every gun in every competition, and every duty holster would have it. It just ain't so.

[Jim Watson]

That is the "If you are so smart, why aren't you rich?" argument.

Glockish rifling is produced on large expensive hammer forge machines in reach only of large companies producing huge numbers of barrels.

High end competitive shooters use guns from smaller makers or production guns accurized with aftermarket barrels. Those small shops can't afford the big Krupp machines. Button and cut rifling are precision operations but the tooling is affordable if you are a serious craftsman and businessman.
One article calls Krieger a large barrelmaker. They have 26 employees and made 15000 barrels that year. Peanuts for Glock or Remington.

[jimbob86]

One article calls Krieger a large barrelmaker. They have 26 employees and made 15000 barrels that year. Peanuts for Glock or Remington.

But does anybody, the gaints included, make a polygonal barrel for a "target gun" that anybody that is not paid to use, actually uses? IF a polygonal rifled barrel was actually better than traditonal rifling, folks that really need top velocity and accuracy would be using them. They are not using Krieger because they have thing for small companies, but because the product works better.

[Ocraknife]

I'm just curious, how much cheaper is it to make a polygonal rifled barrel? 10% or 20% how much of a price of an average Glock or HK does a barrel command?

Some of the HKs are pretty pricey it doesn't seem that they'd cut corners on the barrels.

If it were all about cost it seems to me that hi-point, rossi and other budget manufacturers would all be using polygonal rifling.

My ultimate point is, perhaps both have their merits and fill a certain set of requirements so "better" depends upon the particular use case. Just a thought.

[Radny97]

Just noticed that tanfoglio uses polygonal rifling in some of its high end competition pistols, so that throws another wrinkle into this.

[Limnophile]

I've seen the better velocities in print, but again without much why info to back it up.

Presumably the interaction of the bullet and the polygonal barrel produces less friction.

[Rembrandt]

Styer, Desert Eagles, Stahls, are other European manufacturers use polygonal rifling. There are also different styles, some are completely smooth looking like a Wankel rotary piston and others have small rounded bumps where as button rifling lands are sharp and pronounced.

Have been told that conventional lands will allow gases to escape between the bullet and land. (maybe true, but probably a hard thing to measure any significant difference) Thus allowing the bullet to expand and conformed to a 100% seal before exiting the barrel. It also reduces barrel wear and makes cleaning easier.

[Radny97]

Here's an interesting article at least trying to look at the differences.

http://www.ballisticsbytheinch.com/rifling.html

My conclusion--there may be a slight increase in velocity using polygonal rifling for most but not all loads of ammunition. The increase is generally not enough to really matter and may not even be statistically significant.
So . . . the question is still open on the issue of any accuracy advantage (which probably is more dependant on the manner and quality of the type of polygonal rifling utilized rather than polygonal rifling in general.)
Ultimately it appears to me that polygonal rifling is a manufacturing process that yields cost savings to large scale operations. But as to the consumer, it does not offer any systemic advantage over land and groove rifling (but it doesn't create any disadvantage either).
It still comes down to the quality of the gun made, no matter the type of rifling used.

[pax]

Poly rifling is not supposed to shoot lead, but i've never heard a good why.

With polygonal rifling, you tend to get less fouling overall. But the fouling you do get builds up on the mating surfaces and not in the grooves. This narrows the passage through the barrel, which in turn can produce much higher pressures than the barrel is designed to contain.

It's different from traditional rifling because when you shoot bare lead through traditional rifling, the lead tends to build up in the grooves. It does not narrow the passageway.

It's tempting to think that this only means we could shoot lead bullets through a polygonal barrel as long as we clean it more often, but it's not quite that simple. The amount of lead deposited with each bullet is wildly variable, as are the pressures from various rounds. This means there's really no reasonable way to to deal with it, except to avoid it entirely. Other than "don't shoot lead bullets in polygonal-rifled barrels", there just isn't a rule of thumb that can be trusted.

So even though you might go for years without a problem, you also might not -- when lead deposits build up on the mating surfaces, the barrel can bulge or burst without warning. That means the only truly safe solution is not to shoot bare lead in polygonal barrels.

pax

[Roland Thunder]

Doesn't the Kahr PM9 have polygonal rifling?

[Jim Watson]

It's different from traditional rifling because when you shoot bare lead through traditional rifling, the lead tends to build up in the grooves. It does not narrow the passageway

I have looked and looked at barrel drawings and cannot find a "passageway."

Since current practice is to make bullet diameter = groove diameter and SAAMI specifies the barrel cross sectional area including the grooves, heavy leading in the grooves does indeed "narrow the passageway."
I have not heard of barrel damage from such accumulation, except from the unwise practice of "shooting out the lead" with jacketed bullets.

But then I am not really certain that I have actually heard of barrel damage from leading of a Glock barrel, either.
I have heard CLAIMS that leading caused damage to a Glock barrel, but it is kind of like "fired out of battery" and "detonated", it is normally an ex post facto attempt at explaining away bad judgement or lack of hard facts.

Has anybody ever run a controlled experiment to lead up a Glock barrel to a known degree and see what happened?

[pax]

Jim,

Look for a book titled "The Glock in Competition". It has a chapter written by a forensics engineer (Mark Passamaneck) who has studied the topic very thoroughly, and his discussion covers Glock leading issues in detail. The chapter is titled, “The Exploding Glock, Fact or Fiction?”

pax

[chris in va]

Glock has a different version of poly riflng than most. It's just a smoothbore with some rounded bumps thrown in.

I used wheelweight lead exclusively in the 21 I had, probably 1000 rounds at least. At first I was really cautious and swabbed the barrel every couple mags, but soon realized it was pointless as the bore was a mirror. Never had a leading issue with it.

Now my Kahr K9 on the other hand...yikes. One mag and that was all she wrote. It has the more traditional style poly rifling and does not like lead. Needless to say it doesn't go to the range much.

[JohnKSa]

Has anybody ever run a controlled experiment to lead up a Glock barrel to a known degree and see what happened?

Yes, most definitely. The book pax referenced discusses the issue in detail.

The author of the chapter in question began researching the problem after blowing up one of his own Glocks. He had the means at his disposal to do so and I get the feeling that he initially felt he would be able to show that there was a problem with the pistol.

After determining what had caused the problem, he then tried to develop a reliable process/rule for using lead bullets that would eliminate the possibility of a catastrophic incident. Instead, the result was that he chose to shoot only plated or jacketed bullets in Glock factory barrels from then on.

His testing (involving shooting many thousands of rounds fired with instrumentation) revealed that the leading progressed at an alarmingly rapid rate in some Glocks while other apparently identical Glocks behaved much differently when using the same ammunition.

I have looked and looked at barrel drawings and cannot find a "passageway."

Since current practice is to make bullet diameter = groove diameter and SAAMI specifies the barrel cross sectional area including the grooves, heavy leading in the grooves does indeed "narrow the passageway."

This issue is addressed as well. The Glock bores have a smaller cross-section than a typical land and groove barrel and all else being equal will tend to have discharge pressures 5% to 7% higher as a result. That's before any leading at all.

[happyguy]

I have never considered the type of rifling when choosing a firearm.

I know, I'm no help at all.

Sorry.

[Jim Watson]

I will see if I can find the book on interlibrary loan so I can read about Mark's leading tests and save $40.

Is Glock USA a SAAMI member?
If Glock 9mms do not have a minimum bore/groove cross sectional area of .0967 square inches, they do not meet SAAMI specification. The standard is 6 groove but they give an area spec for freak rifling plans.

[Jim Watson]

I got the book and read Mark's chapter on the liabilities of lead in Glock "polywobbly" barrels. I follow his reporting and logic.

[MrWesson]

Poly rifling is not supposed to shoot lead, but i've never heard a good why. It is aldo said to be more accurate and have slightly better velocities

.

I'll bite.

This is personal experience/test using a Glock 26 with my sized cast bullets.

First 50-100 rounds were no big deal. Accuracy remained similar to with jacketed.

Things got interesting at about round 175 accuracy went to hell. Significant leading in the barrel to the point where I had to stop. By significant I mean somewhere between normal and turning a rifle barrel into a shotgun bore.

Unsafe? I'm no expert but id imagine an increase in pressure based on simple physics. Blow up the gun before you notice something's up? If you're a very poor shooter who wouldn't notice a group going from 3" to 9" its possible.

Either way its not ideal IMO.