Does a gain-twist polygonal barrel really give such a huge velocity boost?

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[ARCHIVED THREAD] - Does a gain-twist polygonal barrel really give such a huge velocity boost?

Posted: 3/9/2005 6:31:01 AM EDT

An Arms Tech in AZ rifle was reviewed by writer Al Paulson. They had a 9.5 inch gain-twist polygonal barrel from Walther. They got 2705fps with M193 55 grain ammo. They also tested a Colt M4 with a 14.5 inch barrel and got 2697fps. They also claim that a 14.5 inch gain-twist polygonal Walther barrel would likely have as much velocity as a 20 inch standard barrel. I find this hard to believe. And if it happened, I would suspect they had a tight match chamber while the Colt obviously had an MG chamber. If their results are true, and there is no funny business, then it seems pretty revolutionary to me. Do you buy it?

I mean, if a 14.5 inch could have 20 inch speed, that would be earth shattering in my book, and I would HAVE to have it. Yet my bullshit detector is clipping the meter.

Posted: 3/9/2005 7:05:50 AM EDT

[#1]

Quoted:
An Arms Tech in AZ rifle was reviewed by writer Al Paulson. They had a 9.5 inch gain-twist polygonal barrel from Walther. They got 2705fps with M193 55 grain ammo. They also tested a Colt M4 with a 14.5 inch barrel and got 2697fps. They also claim that a 14.5 inch gain-twist polygonal Walther barrel would likely have as much velocity as a 20 inch standard barrel. I find this hard to believe. And if it happened, I would suspect they had a tight match chamber while the Colt obviously had an MG chamber. If their results are true, and there is no funny business, then it seems pretty revolutionary to me. Do you buy it?

I mean, if a 14.5 inch could have 20 inch speed, that would be earth shattering in my book, and I would HAVE to have it. Yet my bullshit detector is clipping the meter.

That is what I am going for too. The mcmillian M89 had an 18 inch polygonal, and it had pretty decent numbers too, but they were at least believeable. I think something like 2700 with 168 grain hp?

14.5 getting under 2950 with mil pressure 55 grain is BS. That 14.5 barrel must have been shot out bad. Something funny is going on.

Snieder(sp?) barrels were in the intial prototype runs of the SPR. Apparently, they didn't see a cost versus performance advantage because they ended up choosing Douglas for the barrel.

Then again, I don't know that cost was much of an issue. The SPR package costs about 5 grand by the time you get the pelican case and cleaning supplies, etc.

Posted: 3/9/2005 12:06:23 PM EDT

[#2]

The theory is that the polygonal bore creates a better gas seal, thus better velocity. I have a custom upper that GA Precision built for me with an 18" Schneider barrel. I am planning on getting a chrony at some point and looking at different loads, but haven't gotten around to that yet. I will tell you that one of the biggest advantages I have seen for poly bores vs standard land and groove rifling is the ease of cleaning. Typically, I see a little more carbon fouling in my poly bore guns (HK USC, 2 HK USP pistols) but there is little, if any, copper.

Posted: 3/9/2005 1:11:17 PM EDT

[#3]

I believe the gain-twist is the chief cause of the increased velocity. Something about reducing velocity lost by bleeding energy in the first few inches to start the bullet's rotation. If the bullet's rotation is more gradual then less energy is "wasted" on rotation and therefore available for forward motion. I'm no physicist so I could be off but that's the way I understood it.

Posted: 3/9/2005 6:00:44 PM EDT

[#4]

FYI: S&W is using this kind of rifling on their new .460 S&W mag. It is their new velocity champ.

Posted: 3/9/2005 6:18:31 PM EDT

[#5]

I think the S&W just has regular polygonal rifling like a Glock or HK.

Posted: 3/9/2005 10:59:47 PM EDT

[#6]

The poly rifleing would be a plus in the cleaning dept. Three or four swipes through my USP bbl and I'm done!

Cold hammer forging would also be a huge plus. Those of you with select fire would appreciate this more than those of us with semi only. But everybody would definately benifit from more durability. I have never worn out a bbl but some of the accuracy is beginning to degrade a bit.

Posted: 3/10/2005 4:15:01 AM EDT

[#7]

If there is misinformation on their velocity, why should I believe the barrel outlasts a chrome-lined 3:1? That also sounds unlikely. Once again, if there was some magical barrel material that lastes 3 times as long, David Tubb would be using it to win competitions. People like him are terrified of a barrel going before the end of the season. The more unlikely something is, the more proof one should demand.

Posted: 3/10/2005 4:21:07 AM EDT

[#8]

Regarding barrel life of poly bore barrels, they supposedly last longer because there are no cut edges to wear like in a land and groove rifled barrel. I am no expert on barrels, metallurgy, etc but the theory is sound.

Posted: 3/10/2005 4:29:35 AM EDT

[#9]

They probably do last longer. But do they last 3 times longer as stated?

Since barrels wear out first due to throat erosion and not rifling going bare, I am not sure why this barrel's throat would last 3x longer than a chromed-steel one, or someone else's stainless steel one.

Posted: 3/10/2005 11:24:29 AM EDT

[#10]

As far as polygonal barrel life goes, and with my dealings with Lothar Walther in Georgia, It has been stated to me that progressive polygonal barrels last about 40% longer than chrome-lined. 300% longer is stretching it quite a bit.

Posted: 3/10/2005 11:27:00 AM EDT

[#11]

Also, as far as polygonal barrel life is concerned, they do last longer becuase no metal is actually cutting into the bullet, however, polygonal barrels are just slightly less accurate than cut rifled barrels. The reason relayed to me was the polygonal bore profile somewhat deforms the overal shape of the bullet, while cut rifling only minorly cuts into the bullet to guide it for twisting but the overall shape remains undeformed.

Posted: 3/10/2005 12:00:52 PM EDT

[#12]

Quoted:
An Arms Tech in AZ rifle was reviewed by writer Al Paulson. They had a 9.5 inch gain-twist polygonal barrel from Walther. They got 2705fps with M193 55 grain ammo. They also tested a Colt M4 with a 14.5 inch barrel and got 2697fps. They also claim that a 14.5 inch gain-twist polygonal Walther barrel would likely have as much velocity as a 20 inch standard barrel. I find this hard to believe. And if it happened, I would suspect they had a tight match chamber while the Colt obviously had an MG chamber. If their results are true, and there is no funny business, then it seems pretty revolutionary to me. Do you buy it?

I mean, if a 14.5 inch could have 20 inch speed, that would be earth shattering in my book, and I would HAVE to have it. Yet my bullshit detector is clipping the meter.

There was a thread within the last month on the AR Discussions board about this very topic. Do a serach on COMPAK.

Chrono'd results weren't that impressive -- the COMPAK-16 upper velocity (10.5" barrel) fell right between conventionally rifled 9.5" and 14.5" barrels. The COMPAK-16 barrel didn't come close to matching 14.5" M4 barrel velocities.

What we need to see are more independent write-ups on this system to find out where the truth lies.

Posted: 3/10/2005 12:26:05 PM EDT

[#13]

I found that post. It was by Chris Bell and it was very well done.

I am all for polygonal barrels. David Tubb switched to them. I always liked that HK and Glock used them.

Posted: 3/13/2005 12:42:33 AM EDT

[#14]

So it degrades accuracy?

i have read some where it improves accuracy

[ARCHIVED THREAD] - Does a gain-twist polygonal barrel really give such a huge velocity boost?

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