Gain twist

Huckleberry

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Ordering a gain twist barrel for the 338. Where to start and finish at is the discussion. I'm thinking 10 twist to start and 6 twist at the end. Should work well with the heavier long for caliber, lathe turned bullets. What are you guys thinking?
 

jasonk

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Re: Gain twist

How long's it gonna be, 60"?

10 to 6....not sure you can gain that quick.

I could be wrong, but I think on 338 that a 10 to 9 would be plenty.
 

Noel Carlson

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Re: Gain twist

Huckleberry,

That would be fine for use with a 6.5, or 7.0 caliber ZA.

Best,
Noel
 
A

Augustus

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Re: Gain twist

I have ordered a Bartlien 375 13-6.5 twist. How it will work nobody knows. Thats the fun part!!!
 

Jeffvn

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Re: Gain twist

I (my gunsmith) took possession of one with sufficient twist to hopefully stabilize the 7.0 caliber 338s. I'm still waiting on a reamer to chamber the barrel, but that should be to my smith in a couple of weeks then I hope to have a rifle to go out and test. reports to follow when I finally get it in my hands and put some rounds down range.

Jeffvn
 

Huckleberry

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Re: Gain twist

Jason - 31" - 32" max. I could have went with more twist than that if I wanted.

Jeff - What twist did you go with for the 338 project? Lapua or Norma?
 

C.K

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Re: Gain twist

Jeff,

Did you get a chance to look at the bore finish of your barrel??
 

Rafael

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Re: Gain twist

Not to be a dissenter, but what do you gain with a gain-twist barrel?
I strive to understand all things that I do not....and am interested in this.
 

Tyler Kemp

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Re: Gain twist

Well, I really am just guessing, but wouldn't it require less pressure to start the bullet at a gentle (relatively) spin, then ramp it up once pressure has gone way down?
 

jasonk

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Re: Gain twist

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jasonk</div><div class="ubbcode-body">How long's it gonna be, 60"?

10 to 6....not sure you can gain that quick.

I could be wrong, but I think on 338 that a 10 to 9 would be plenty.
</div></div> <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Noel Carlson</div><div class="ubbcode-body">Huckleberry,

That would be fine for use with a 6.5, or 7.0 caliber ZA.

Best,
Noel</div></div> <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Huckleberry</div><div class="ubbcode-body">Jason - 31" - 32" max. I could have went with more twist than that if I wanted.

Jeff - What twist did you go with for the 338 project? Lapua or Norma?</div></div>

I truly had no idea that you could "gain" twist that fast...wow!

I assumed it was much less, like 10 to a 9 or maybe 10 to an 8.

I appreciate the education....just when you think you know something!
 

lanwickum

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Re: Gain twist

As I understand, doesn't tear up the bullet as much with a sudden twist forced on it. Although the rifleing angles changes as the bullet passes down the tube.....
Never tried one, but they do get my attention as something I would like to try out someday.
 

Jeffvn

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Re: Gain twist

Mine is a ..... 12" to a 5.4" at the muzzle. The tube is 32" long.

Nope I had no chance to look through the bore it went straight to the smith from Frank at Bartlein. I'll get plenty of chances to stare at it once it gets delivered.

JeffVN
 

krw

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Re: Gain twist

Man, I didn't realize you could have that much increase (Gain). I think you should call some of the bbl mfg's and find out 100% absolutely for sure. Keep us informed.
 

Rafael

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Re: Gain twist

Thanks, gent's.
Yes, I had heard the theory of reduced pressure because of reduced twist. I have a bit of trouble with that one since the bullet is entering the rifling at very low speed. Unless you let it jump alot, the bullet starts out at zero and speeds up as it travels down the barrel.

Just trying to get my head around the advantage since the bullet starts at such a low speed the twist barely has an effect.
If it entered the bore at 2600fps it would make alot more sense.
 
A

Augustus

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Re: Gain twist

There is fear that the bands on the banded solids will not tolerate the forces generated when entering a very tight twist barrel. Hence the use of gain twist barrels. Actually I have never seen or know anyone who has seen the bands fail on Noels banded bullets. When all of the tests are complete it MAY be determined gain twists are not needed. All this is still up in the air and we wont really know until a lot of rds have been sent downrange in both gain and standard twist barrels.
 

Noel Carlson

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Re: Gain twist

Rafael,

You are correct about the idea of a high-gain twist reducing "pressure" being conceptually faulty. It does not have any measurable effect.

Augustus is on the right track, however, with a gas-seal concern. What he means by the bands "failing", is that the primary (single) rear band opens up a swaged gap on the idling side of the land/band interface. If this happens, hot gases will rapidly vaporize the copper band, and all sorts of problems are initiated from that point.

The objective is to maintain a seal, but with the minimum amount of friction. A 6.0 caliber 338 in a constant 9.0" twist <span style="font-style: italic"> </span> barely <span style="font-style: italic"> </span> meets this requirement. A longer projectile would fail to seal instantly, and the design paradox is that the longer projectiles (6.5 & 7.0 caliber) need an even tighter twist.

There are other potential, or real, advantages having to do with shooter comfort (which is established), and barrel harmonic amplitudes (which is not proven).

Best,
Noel
 

Huckleberry

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Re: Gain twist

Tony Boyer, the Hall of Fame benchrester, is using a gain twist barrel and from what I understand, some cannon, artillery, etc. use it. It has been around for at least a century or more.

The barrel also has a tapering effect at the muzzle since more twist equals more metal in the bore over a given distance. Some people also think that the gain twist is more gentle, if you will, to the bullet (jacket/lead core construction). I guess that time will tell.

I will be ordering mine once I figure out what receiver I will be using.

Jeff, what time frame did your barrel take from ordering to completion?
 

gugubica

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Re: Gain twist

Noel, why not start out with a smooth bore?

Seriously, you would be able to get a REALLY good seal between the bands and the bore. Then the projo would contact the lands, cut into them and stabalize the bullet. But it would not start cutting and twisting until the majority of the acceleration/burn has been completed. Any additional burn would keep it from slowing when the lands start cutting, but the gas seal would not be as important at that point (projo is already moving along nicely) and the lands would only serve to twist/stabilize.

Sorry for the rudimentary drawing, but,

smoothtotwist.jpg
 

2RECON

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Re: Gain twist

@ Noel,
mayby i´m wrong but please help me to understand it RIGHT....

Just to calculate:
375 Chey_tac and 330 Lehigh Bullets....

Ok, it´s clear that you´ll need a gain twist barrel because of the forces working against the driving bands..(space of full contact to the rifeling)
There must be a relation between how FAST you whant to drive that Bullet though the bore to the needed twist...right?
So, if i´m NOT going to get about (don´t know exactly) 3300fps using that named Bullet, but say just about 2800fps....( Thinking about another Case to work with...)
Do you think that a "standard" 12" twist is working with a 330LH..??

Hope my bad english is good enough...

2RECON
 

Noel Carlson

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Re: Gain twist

gugubica

That is a great solution to throat erosion, but this projectile is designed with a duplex alignment band for axial indexing off of the bullet, rather than the case shoulder. A smooth-bore lead could indirectly cause in-bore cant, which is a mojor source of dispersion.

-Noel
 

Noel Carlson

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Re: Gain twist

2Recon,

As I understand the Lehigh design, the forward band has an interference fit, and the rear is full supra-groove diameter with a large engraving footprint. There is no purpose served with a gain-twist that I can think of, and I would go with whatever they recommend for twist-rate.

I hope this answers your question. If not, try me again.

Best,
Noel
 

Shady_Jay

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Re: Gain twist

I have used gain twists in .308 with very good results.
 

Huckleberry

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Re: Gain twist

How about a little more detail.
Who made the barrel or barrels? What twist rate? Are you still using them?
 

C.K

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Re: Gain twist

The barrels that are being made to test noels bullets are being manufactured by Bartlein. I know they just got done with a run of 338 barrels hence jeff just getting his. The .375 barrels are bored and waiting rifling(as I was told thursday). As Augustus said his is coming in 13 to 6.5, mine is going to be 12 to 6 and I don't know what the other ones are coming in at.

I know some of us are trying some different throat angles on the reamers, will it make a difference?? I got my theory based on doing this on BMG rifles but these were with standard bore riders and not this type of design. If it is beneficial it might only be for a couple hundred of rounds until the bore deteriorates and you start chasing the lands, but you never know.
 

Huckleberry

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Re: Gain twist

Are you changing the lead angle?

I went with a 1 degree on my 338 reamer. I order zero freebore on all of my reamers now and throat accordingly. Crane is also doing some experimenting on the 300 winny but I don't know what the details are and don't know if it has been successful.
 

C.K

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Re: Gain twist

yes, I should of worded the last post differently, I bought a separate throat reamer with a 1 degree lead angle.