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Author Topic: Barrels - Polygonal vs. Rifling  (Read 10254 times)

StevenTing

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Barrels - Polygonal vs. Rifling
« on: January 26, 2012, 11:17:41 AM »
I know how rifling works.  Bullets are slightly larger than the barrel, which when fired, get squeezed and take the form of the rifling, which causes the bullets to spin for stability.  I think the same concept works for Poly barrels.

But why are there two types of barrels?  Is one better than another?  Since HK uses poly barrels, they must be better.  Crusader uses them too. :neener  If one turns out to be better, how come all guns aren't like that?  Is it merely a cost issue?
Utah


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huey148

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Re: Barrels - Polygonal vs. Rifling
« Reply #1 on: January 26, 2012, 11:22:40 AM »
I think Gun Doc is the best authority on it....Joe?

And Glock uses poly barrels as well....
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Thernlund

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Re: Barrels - Polygonal vs. Rifling
« Reply #2 on: January 26, 2012, 11:40:56 AM »
My understanding is that polygonal rifling offers less drag and a better gas seal.

They're harder to make because unlike a traditional rifling, which is simply cut into the barrel, polygonal rifling is hammered into the barrel.  Hammer forging machines are apparently very very expensive.


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JesseL

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Re: Barrels - Polygonal vs. Rifling
« Reply #3 on: January 26, 2012, 11:54:42 AM »
To understand the different types of rifling you have to understand the different ways gun barrels are made.

Conventionally, barrels start as a long steel cylinder that's drilled (using a gun drill - drilling long straight holes is tricky in itself), and then the rifling is formed by pulling a single point cutter (several times for each groove), a rifling broach, or a carbide rifling button through the bore.


That gives you your conventional land-and-groove style rifling. The equipment can be purchased for a couple thousand dollars or even made from scratch in a simple shop.

In more recent years, hammer forged barrels have become popular. These start with a short fat cylinder of steel which is hammered around a mandrel which is essentially a negative of the shape of the inside of the barrel. It's necessary for these to form polygonal rifling due to the way the steel is formed around the mandrel and the necessity of being able to pull out and reuse the mandrel when the process is complete.

Steyr Firearms - How Steyr-Mannlicher Hammer Forges Their Barrels


Hammer forging machines can produce barrels quickly and cheaply, but the machines themselves cost millions of dollars.

Polygonal rifling has many advantages over conventional rifling in terms of bore friction, gas sealing, and minimizing bullets distortion; but it's not necessarily ideal for all barrels when issues of the scale of manufacture and absolute accuracy come into play.
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Re: Barrels - Polygonal vs. Rifling
« Reply #4 on: January 26, 2012, 12:34:39 PM »
The guys at a local gunshop claim that polygonal rifling also lowers the risk of forensic matching.

I figure they're pulling my chain, on the basis that there would still be microscopic scratches in the barrel that would lead to forensic matching?

Are they pulling my chain?

Thernlund

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Re: Barrels - Polygonal vs. Rifling
« Reply #5 on: January 26, 2012, 12:39:31 PM »
Well, that's what Wiki says. 

http://en.wikipedia.org/wiki/Polygonal_rifling#Forensic_firearms_examination

Seems logical, but who knows except real forensic examiners?  :shrug 


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Re: Barrels - Polygonal vs. Rifling
« Reply #6 on: January 26, 2012, 12:52:46 PM »
The guys at a local gunshop claim that polygonal rifling also lowers the risk of forensic matching.

I figure they're pulling my chain, on the basis that there would still be microscopic scratches in the barrel that would lead to forensic matching?

Are they pulling my chain?


Nope, it's true. Ballistic matching is also of limited value if the gun has been fired more than a few times or seriously cleaned since firing the bullet you're trying to match. Fouling deposits, the effect of thousands of PSI of hot gas, and bullets sliding past at hundreds of miles per hour will change those microscopic scratches pretty regularly. It's just not as reliable as CSI would have you believe.

Well, that's what Wiki says. 

http://en.wikipedia.org/wiki/Polygonal_rifling#Forensic_firearms_examination

Seems logical, but who knows except real forensic examiners?  :shrug 


Even the real forensic examiners might not be real inclined to share the whole truth on the matter. They've got their livelihood tied up in continuing the public faith in the scientific perfection of their methods.
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Re: Barrels - Polygonal vs. Rifling
« Reply #7 on: January 26, 2012, 01:24:17 PM »
The other advantage Polygonal Barrels have is that the Barrel is Hammer Forged as mentioned.  That's an advantage in and of its self. It's a better result regardless of the type of rifling.
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Re: Barrels - Polygonal vs. Rifling
« Reply #8 on: January 26, 2012, 03:01:09 PM »
There are advantages of both rifling types and also some disadvantages.  There are a few different ways to "cut" conventional rifling...some better, and more expensive than others but as far as I know poly rifling can only be hammer forged. I do prefer poly rifling in pistols but rather have conventional rifling in rifles for a few reasons.  I wouldn't make a blanket statement that one is better than the other but the both have their places.
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StevenTing

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Re: Barrels - Polygonal vs. Rifling
« Reply #9 on: January 26, 2012, 03:08:27 PM »
There are advantages of both rifling types and also some disadvantages.  There are a few different ways to "cut" conventional rifling...some better, and more expensive than others but as far as I know poly rifling can only be hammer forged. I do prefer poly rifling in pistols but rather have conventional rifling in rifles for a few reasons.  I wouldn't make a blanket statement that one is better than the other but the both have their places.

What are those reasons?
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Re: Barrels - Polygonal vs. Rifling
« Reply #10 on: January 26, 2012, 07:15:25 PM »
Poly rifle barrels can be very picky and in my (limited) experience they don't like the heavy bullets...preference was for long, light to mid-weight projectiles.  Pistols are of course different and the poly barrels love the .36 caliber & larger projectiles.  Very easy to clean, consistant velocity, excellent gas seal, increased accuracy and longer life...but there are other reasons beside cost that poly barrels aren't more common in rifles.

What are those reasons?
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Re: Barrels - Polygonal vs. Rifling
« Reply #11 on: January 26, 2012, 07:26:27 PM »
I don't know, they've been working REALLY well in the Broadswords.  I don't know the exact numbers, but Gundoc could tell you.  Our customers are getting insane accuracy from them, like a three inch shot group at 600 yards or something crazy like that.
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Re: Barrels - Polygonal vs. Rifling
« Reply #12 on: January 26, 2012, 08:59:05 PM »
Bullet weights have little to do with rifling type... but the rate of twist.
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Re: Barrels - Polygonal vs. Rifling
« Reply #13 on: January 26, 2012, 11:57:38 PM »
So are all Crusader barrels now Poly barrels?  Including the "bones"?  And what twist rate are the Crusader barrels?

The idea of a "better seal" or seat with the rifle makes sence to me....  It could lead to better accuracy.... but it seems to me that with less leading or other build up that it would make the barrel more consistent in placing the bullets.  That would be the major advantage I could think of.  :shrug

I am just learning about rifleing and the importance of bullet weight with it.  When I did shoot rifles I just went for the same brand and type of bullet for the consistency of shot placement.  I am just now at 36 learning of the reasons and science behind it.
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mattitude

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Re: Barrels - Polygonal vs. Rifling
« Reply #14 on: January 27, 2012, 12:17:10 AM »
With cut rifling...yes, but poly is much lower friction and doesn't have not as much "bite" that the heavier slugs get more push than twist and if th projectile has less contact area there is more chance for runout.  I'm probably clear as mud because I have difficulty explaining things.  Manufacturing poly barrels are no more expensive than a regular CHF barrel...but if they are superior than why aren't more manufacturers producing them?  IMO the benefits don't outweigh the negatives as they are picky eaters in high velocity rifles, but in pistol calibers they rock out.

Bullet weights have little to do with rifling type... but the rate of twist.
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Re: Barrels - Polygonal vs. Rifling
« Reply #15 on: January 27, 2012, 02:28:54 AM »
I agree with pretty much everything said here, but I am surprised no one mentioned the lead "issue".  Remember poly barrels + Pb = boom!
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Re: Barrels - Polygonal vs. Rifling
« Reply #16 on: January 27, 2012, 03:16:57 AM »
I agree with pretty much everything said here, but I am surprised no one mentioned the lead "issue".  Remember poly barrels + Pb = boom!

While I'm not an expert, I think that might be more of an issue of twist rate vs slug hardness/density. Faster twist = more lead stripped off the slug = more fouling = etc.

Another idea is that it might be their lawyers telling them to add the warning as a way of avoiding liability. Bubba uses his old fishing weights to cast slugs..get where I'm going with that? (no offense intended)

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Re: Barrels - Polygonal vs. Rifling
« Reply #17 on: January 28, 2012, 12:54:41 AM »
The issue is that the polygonal rifling has less room for fouling because you are in swaging the bullet to the bore's size and shape.  The lead fouling will obstruct the bore a little bit with each shot and eventually up the pressure to a dangerous level.  I have seen (Glocks in particular) case failures and one kb as a result of a diet of lead.
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Re: Barrels - Polygonal vs. Rifling
« Reply #18 on: January 28, 2012, 06:35:23 AM »
Manufacturing poly barrels are no more expensive than a regular CHF barrel...but if they are superior than why aren't more manufacturers producing them?

Expense of investment in rifling machinery?  If you have cut or button rifling machinery that works adequetly, then why re-invest millions in new machinery to make rifling in a different way if consumers won't notice the difference?
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Re: Barrels - Polygonal vs. Rifling
« Reply #19 on: January 28, 2012, 08:06:44 AM »
That's not the question...the question is why doesn't say, FN produce poly barrels?  They already have the HF machinery so it shouldn't be much more than a different mandrel and a reprogram so the investment would be minimal.  So if that is the case, why aren't manufacturers producing poly barrels if they are better than land and groove rifling?

Expense of investment in rifling machinery?  If you have cut or button rifling machinery that works adequetly, then why re-invest millions in new machinery to make rifling in a different way if consumers won't notice the difference?
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seanp

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Re: Barrels - Polygonal vs. Rifling
« Reply #20 on: January 28, 2012, 01:10:00 PM »
That's not the question...the question is why doesn't say, FN produce poly barrels?  They already have the HF machinery so it shouldn't be much more than a different mandrel and a reprogram so the investment would be minimal.  So if that is the case, why aren't manufacturers producing poly barrels if they are better than land and groove rifling?


Yeah...  Like... What I said again:  If you got 50 machines making cut rifling at a certain rate, why dust all that and make only poly barrels on one or two machines?  It doesn't make fiscal sense man.

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Re: Barrels - Polygonal vs. Rifling
« Reply #21 on: January 28, 2012, 02:22:17 PM »
Yeah...  Like... What I said again:  If you got 50 machines making cut rifling at a certain rate, why dust all that and make only poly barrels on one or two machines?  It doesn't make fiscal sense man.

Hey man, why don't GM make Toyotas?  They both cars, right?

Well, I'm pretty sure the UAW isn't the reason FN doesn't use polygonal rifling.  I've been to their plant in Columbia, SC, and it's non-union.
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Re: Barrels - Polygonal vs. Rifling
« Reply #22 on: January 28, 2012, 05:59:24 PM »
If it ain't broke don't fix it?


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StevenTing

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Re: Barrels - Polygonal vs. Rifling
« Reply #23 on: January 28, 2012, 07:01:03 PM »
Stop crapping in my thread or I'll give you each a 2 day ban.
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Re: Barrels - Polygonal vs. Rifling
« Reply #24 on: January 28, 2012, 09:09:33 PM »
Thread crap has been shoveled (deleted) on Steven's behalf.  This is a good thread.


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EDIT:  Another post deleted and someone got a ban.  Do not thread-crap means DO NOT THREAD-CRAP.  WTF?
« Last Edit: January 28, 2012, 10:38:26 PM by Thernlund »
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