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9/22/2017 12:11:25 AM
Posted: 8/3/2005 8:32:08 PM EDT
I saw in some gun rag not too long ago about a short barrel AR w/ gain twist rifling. I can't remember the manufactorer or the publication, but the article seemed to list some advantages to it.

Less barrel wear, and most importantly IMO much better velocity-14.5" barrel close to 20" velocity(after all, that seems to be the big debate over to have short barrels or not).

Is there a catch?

Otherwise, it seems to me that this would be a good answer to have the best of both worlds (short barrel w/ high enough velocity).
Link Posted: 8/3/2005 9:11:26 PM EDT
bump.
Link Posted: 8/4/2005 2:08:46 AM EDT
That was ARMSTECH's M-4. I wish someone would make chrome lined gain twist polygonal ar barrels. be interesting to see how they perform.
Link Posted: 8/4/2005 7:41:47 AM EDT
I dont believe the claims made. If I remeber correctly someone said in acuality they dont produce as much velocity increas as advertised.
Link Posted: 8/4/2005 9:39:26 AM EDT
The Noveske uppers are stainless steel with polygonal rifling.
Link Posted: 8/4/2005 10:39:15 AM EDT
[Last Edit: 8/4/2005 10:46:12 AM EDT by jmart]

Originally Posted By Feedingcannibal:
The Noveske uppers are stainless steel with polygonal rifling.



And some claim the poly rifling here gives a velocity gain. So who's to say AT claims are wrong? BTW, Noveske offers both SS and chrome moly -- his barrels are supplied by PAC NOR.

AT needs to get their product out for civilians to try. Lotsa claims made: increased velocity, different SS alloy (not 416R) which has ultra long life and maintains MOA accuracy up into the high thousand round counts (no need for chrome lining), reduced cyclic rate using their gas trap design. I talked to the owner, Joe, several months ago and he said they were pursuing getting their 14" Recon rfile approved for civilian sales -- they would include a permanently attached device to bring the OAL above 16". So far, haven't seen anything. Their website, which is pretty lacking, has remained unchanged for months. I just don't know.

Grant maintains he knows a guy who's getting 2700 fps from a SBR Noveske, using BH 77gr. That claim seemed ludicrous, but if he has a chrono to back it up, who am I to say? At the same time another poster tested an AT Compak16 months ago -- velocities achieved fell right in line with other weapons utilizing conventional rifling -- Compak 16 was faster than 9.5" SBRs but was slower than M4s. I can't remember if that was an early version of the COMPAK 16 which used conventional rifling, or if it was a current-production poly, gain twist barrel.

The sample sizes out there to evaluate these claims are just too small to make any definitive conclusions. We need more samples.
Link Posted: 8/6/2005 4:53:57 AM EDT
Gain twist rifling died at the end of the first world war. Just too expensive to produce and did not produce any improvements in accuracy over conventional fixed twist rates. It was used primarily in large bore artillery to slowly accelerate the rotation of big shells. It led instead to lots of stripped driving bands.
Link Posted: 8/6/2005 5:09:18 PM EDT
I have only read about gaintwist rifling in one new weapon, the S&W .460 revolver. 2200+FPS will be interesting, I handled one last week but it was already sold.
Link Posted: 8/7/2005 5:38:10 AM EDT
[Last Edit: 8/7/2005 5:39:01 AM EDT by twl]
Link Posted: 8/7/2005 8:59:47 PM EDT

Originally Posted By twl:

Not worth the trouble.



Regarding gain twist rifling.... couldn't have spelled it better myself.

Link Posted: 8/8/2005 1:31:24 AM EDT

Originally Posted By twl:
I recently did some research on the matter for a member who wanted to have a polygonal gain-twist rifled barrel in the ABS carbon-fiber barrel.

I called Pac-Nor, and they have sold their gain-twist tooling.

The guy who bought it isn't doing anything with it, and we couldn't get him to let us use it.

Pac-Nor's statements on the matter were that maybe a 2% gain in velocity with certain loads might be attainable in an AR with the gain-twist.

Not worth the trouble.

Polygon rifling is another matter, and may have some benefits due to tight gas seal around the bullet. However, for maximum accuracy work, the 5R rifling and other match-grade cut rifling still seems to dominate the benchrest competitions.

Regarding longevity, I haven't personally conducted any tests to see how many rounds can be shot from a polygon-rifled barrel and still remain accurate. However, I will say that the accuracy deterioration generally comes from throat erosion, and it would seem that the rifling type would not have much effect on that activity. Maybe the harder steel would. But hard steel and rifling types are two different subjects.



Are you considering polygonal twist for SBR carbon fiber barrels?
Link Posted: 8/8/2005 4:54:20 AM EDT
[Last Edit: 8/8/2005 4:59:49 AM EDT by twl]
Link Posted: 8/8/2005 9:39:13 AM EDT
[Last Edit: 8/8/2005 9:40:28 AM EDT by jmart]

Originally Posted By twl:
DevL,

We are currently making a 10.5" SBR barrel in ABS Carbon Fiber process, using the SS Pac-Nor polygon-rifled blank in 1/7 twist, with a suppressor mount.....

It is the same kind of barrel blank that Noveske uses in his barrels.....

This polygon rifled blank option has always been available from us. We've made a few of them, but it hasn't become highly popular yet.....




What kind of velocity does this barrel produce with BH 77 grain OTM? How about Mk 262? And do you know what it would produce if conventionally rifled?
Link Posted: 8/8/2005 10:51:19 AM EDT
[Last Edit: 8/8/2005 11:02:04 AM EDT by twl]
Link Posted: 8/8/2005 11:32:22 AM EDT
[Last Edit: 8/8/2005 11:34:00 AM EDT by Green0]
What I heard seemed to suggest that the polygonal rifling would impart a significant velocity increase and that the gain twist might even compromise the gas seal of the polygonal rifleing as it is a constantly changeing rifleing pattern.

At any rate 2% additional is not really worth the consideration; if anything the purpose of this would be to limit throat errosion and perhaps change recoil characteristics on some small level. The studies just don't exist- from what I understand it is mostly theoretical at this point.

Noveske mentioned 2550FPS from 10.5inch polygonal 1/7's and that sounded like 50-75FPS shy of 14.5inch velocity from std barrels so I'm on board with that.
Link Posted: 8/8/2005 11:37:36 AM EDT
[Last Edit: 8/8/2005 11:46:18 AM EDT by twl]
Link Posted: 8/8/2005 12:15:01 PM EDT

Originally Posted By twl:
Austin,
I think you could help us all out when you get your barrel, by chronographing some 77gr stuff, and letting the membership know what velocities you are getting out of the 10.5 polygon Pac-Nor.

We're working on getting it to you ASAP.

My "seat of the pants" calculations tell me that if the 77gr load will do 2700 out of a 16", it should do about 2500-2550 out of a 10.5. If you add the 100fps from the polygon barrel, that puts it at about 2600 - 2650fps.

That's my ballpark estimate for that load in a polygon 10.5'.
And, when you consider that this load has only a small velocity margin over fragmentation velocity to start with, a 100fps boost would be significant in extending the fragmentation range, especially with a good BC bullet like the 77gr.

So, when you consider that it needs all the help it can get, that extra boost would be valuable to extend frag range from the SBR.

I'm not knocking the polygon barrel.
I'm just saying that a 10.5" is cutting it pretty slim in the velocity department.




twl,

Thanks for giving us your best guess. Don't take this the wrong way, but I am highly skeptical that your poly barrels will achieve 2600 out of a 10.5. I'd be surprised if they hit 2500. Also, I think you lose a lot more velocity than you predict when going down from 16" to 10.5".

cbell was the poster back in Feb that posted his test results with AT Compak 16, which is a 10ish" SBR barrel length. Depending on the load, he was almost 400 fps slower compared to a 14.5" M4 barrel. That didn't dovetail at all with AT's claims, but asuming it's true, I can't see how a Pac Nor would be that much slower than an AT barrel seeing as how they employ very similar technology. Even if GT truly resulted in a step backwards, I don't think it would account for that big a loss.

I'm really looking fwd to chrono data. All of this up to now is just pure theory and educated guessing. But the chronos don't lie.
Link Posted: 8/8/2005 1:51:09 PM EDT
Link Posted: 8/8/2005 5:13:36 PM EDT
[Last Edit: 8/8/2005 5:45:16 PM EDT by jnrifleworks]
I started some 7.62 and 5.56 Polygonal Gain Twist testing a while back.
When the twist rate starts at 1 in 35, the bullet enters a throat with almost straight lands. As the rate of twist increases to 1 in 7, the lands push the forward portion of the bullet's grooves over to one side. When recovering fired rounds, the groove on the bullet is triangular, wider on the front than the base. This is a swage on the diameter of the bullet rather than an inward swage from the initial lead in the throat. Whether this creates a problem or not is still uncertain.
In 2000 A.D., I built a 7.62 bolt gun, 24" SS Poly gain twist, 1 in 50 to 1 in 10 in 20". It shot very well. The side swage issue got my attention, and I attempted to aquire some driving band bullets in 22 and 30 cal, something like the Barnes 50 BMG solids. The bullets never were made, and we went on to other things.
I have two 30 cal 50-10 in 20" Gain Twist SS Polygonal barrels. I just finished one into a 22" AR-10 barrel for a friend. As soon as Armalite gets the upper receivers finished, we'll be testing it.
I built two AR-10 16" lightweights with 50-10 in 12" gains. I have them both here, and will do some chrono testing this week.

Gain twist is very interesting.

As for the 10.5" Poly 7 twist, a friend ran some chrono testing.

Please note that these results were shot back to back, so a total of 10 shots per ammo type, to ensure that there was no error & that the readings were consistent. These are the results of the final series of 5 shots per ammo type:


PLATFORM: M4 w/ Noveske 10.5” Polygonal (1:7 twist)

Lake City XM193 55gr


2528
2887
2821
2665
2539


AVERAGE: 2688 FPS


Lake City M855 62gr


2650
2405
2641
2533
2563


AVERAGE: 2558.4 FPS


Black Hills MK 262 77gr:


2291
2331
2418
2441
2401


AVERAGE: 2376.4 FPS

Hornady TAP NATO 75gr:


2569
2559
2541
2548
2533



AVERAGE: 2550 FPS



----John Noveske

Link Posted: 8/8/2005 5:14:04 PM EDT
the reg cut bbl will be more accurate than the poly cut bbl correct?
Link Posted: 8/8/2005 5:16:25 PM EDT
They are both very accurate.
Link Posted: 8/16/2005 1:48:59 PM EDT
bump
Link Posted: 8/16/2005 2:29:10 PM EDT
found this artical thought some people might be interested.

"Subject: Re: polygonal rifling
From: Gale McMillan <" gale"@mcmfamily.com>
Date: Apr 23 1997
Newsgroups: rec.guns

Barry S Brummett wrote:

# What does "polygonal rifling" mean? How is it different from other
# kinds? Is it a process or a pattern or what? Thanks in advance.

Instead of the rifling being square and hanging down in the bore so that
it can engrave a square notch in the bullet it has flats where the
rifling would be. The bullet is not upset much. Instead of having 6 or
8 sharp knotches it will have small flats that are very unnoticeable.
This makes the bullet fly better in the wind because there is no sharp
edges to bite into a cross wind. The bullet jacket is not deformed as
much so the chances of loose cores are much less. Since there is no
sharp corners to burn off the barrel life is much longer and is
dependent on heat checking alone to end its life. That is one major
reason most barrel makers are not interested in them. It would decrease
their business by half. They are more difficult to make than regular
rifled barrels for a couple of reasons one being they are difficult to
lap and give a cut barrel maker more problems due to tooling."

Gale McMillan

Link Posted: 8/30/2005 7:13:34 PM EDT
Just got some chrono data on the 16" Gain Twist Poly AR-10. The barrel is 1 in 50 to 1 in 10". We were short on time and only fired 5 rounds through it. The barrel had an OPS INC brake on it. I guess it works, but..... I like quiet rifles.

08-30-05 75 F' 1000 ft elev appx 10 ft between chrono and rifles


M118 LR AR-10 16" polygonal gain twist 50-10 SS w/ OPS INC brake

2507
2586
2552
2551
2505<­BR>
average 2540

We shot some other rifles, here is the data. This test was not perfect. It was quick. The chrono was a side note to the Function test on the 10.5" 6.8mm.

M118 LR AR-10 22" 10P SS Smith Vortex same conditions as above

2704
2693
2711
2675
­2688

average 2690

-------------------------------------------------------------------------------------------------------------------

6.8mm SPC Green Box Remington 10.5" 10P SS

W/ KFH

2348
2298
2344
2351
23­19

avg 2330

W/ AAC M47-2000

2424
2400
2376
2390
2­366

avg 2390

-------------------------------------------------------------------------------------------------------------------

Platform 5.56 NMm0 10.5" 7P SS all with US KFH

ammo: MK-262 M1

2480
2466
2474
2448
245­5

avg 2460

ammo: HDY TAP 75gr NATO

2502
2435
2496
2510
2­504

avg 2490

ammo: British NATO SS-109 RORG 89

2697
2633
2617
2681
2658<­BR>
avg 2660

----------------------------------------------------------------------------------------------------------

5.56 NMm0 14.5" AFGHAN 7T 3L SS W/ AAC M47-2000 (left the M4-2000 at the shop)

2887
2935
2943
2911
­2975

avg 2930



Thanks,
----John

Link Posted: 8/30/2005 7:26:57 PM EDT
Link Posted: 8/30/2005 7:42:37 PM EDT
Not sure if anybody is doing anything with it now, but the Germans did that in WWII with the 20mm APCR collapsible driving band projo. It had a tungsten carbide core. The carbide dried up and the production stopped. It has been about 10 years since I read about. I think it was gain twist also. It is on my book shelf, somewhere.....
Link Posted: 8/30/2005 8:05:12 PM EDT
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