.338/408 CT & GSC bullet

[ARMECA]

Hello,

I plan to make a .338/408 CT with a progressive twist to shoot GSC 295 bullet. ( http://www.gsgroup.co.za/338295SP142.html )

Barrel will be a Lothar Walther, 34" lenght
Barnard action, and custom aluminium home made stock.

Just wish to know if someone had ever tried this combinaison, or if it is a good idea ?

Do you think it will have better or worse accuracy/capability than a straight .375 CT ?

Thanks.

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Armeca,

Are you anticipating use of the standard 1: 7" LW exit-twist?

If so, you will want to either tighten it up somewhat, or consider use one of Gerard's shorter bullets. The 6.7 caliber length, of his 295 grain projectile, will limit stability to a muzzle-velocity of <2,600 fps, which totally defeats the purpose of using the CT case (that will easily put your mv over 3,100 fps). This tail style does not tolerate a marginal Sg.

Best,
Noel

 

[ARMECA]

Re: .338/408 CT & GSC bullet

Noel,

Thanks for you answer.

Yes, I plan to use the LW 7" exit twist barrel.
Gerard has told me that a 7.5" or faster twist is OK for his 295 grs SP bullet in .338 LM.
Also Lutz M. advice a 7" exit twist for his LM 105.

As I think Sg is higher with higher velocities I don't understand the stability problem ? Am I wrong ? Can you please explain me ?

Thanks you very much.

Bruno.

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Armeca,

You are correct, Sg measures <span style="font-style: italic">static</span> stability, which is a function of velocity from a given twist, and this does increase at higher exit speeds, but not enough.

The phenomena which which you need to be concerned with is <span style="font-style: italic">dynamic </span> stability, which includes shift in centers-of-pressure, and the associated overturning moment. The dynamically destabilizing factors overcome the statically stabilizing rpm factor, in our tests, where a 7.0 caliber projectile is fired in excess of 2,600 fps from a 21 caliber twist. If the projectile is shortened by 0.5 calibers, an additional 200 fps is gained in stable flight.

To be sure, there are some differences between the LM, GS, and ZA projectiles;

- The 278 grain, 6.4 caliber, LM-105 uses a Haack L-V nose, and a semi-radiused tail. Even from a 1: 7" twist, this bullet is not entirely stable.

- The GS is essentially a tangent ogive, with a tail very close to the LM "Viking" (7.3 calibers), and LM-119 (7.1 calibers). Neither of these Moeller bullets is "stable" from a 21 caliber twist, and that is putting it mildly. They can not hit a 4'x4' target at 100 yards with any consistency, let alone accuracy, and I do not believe increasing static stability will make any difference.

- The 7.0 caliber ZA has a Von Karman nose, and a recurve tail, which produces 0.30 moa groups from a 21 caliber twist <span style="font-weight: bold">provided </span> exit velocity is kept below 2,600 fps.

I can not say for certain what the GS338/6.7 will do from a 7" twist, but do you see the pattern?

Best,
Noel

 

[The Mechanic]

Re: .338/408 CT & GSC bullet

stick with the .375 unless you want to change barrels a lot and be the guinea pig. Lots of good info out on the .375 and it looks great. ONLY advantage I can see is flight time gain and don't see that being a good trade off

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Mechanic,

There is a gain in flight time with the banded-solids, but the greatest advantage is a commensurate reduction in wind-drift. I believe this more than justifies a semi-dedicated barrel, but you are correct about the experimental aspect.

On the up-side, with a LGT equipped rifle, it is a small matter for me to make <span style="font-style: italic">any</span> specific twist work with a simple half-hour programming revision.

Noel

 

[Marriedman1]

Re: .338/408 CT & GSC bullet

Not meaning to start anything but why would you use such great components like the Barnard action and then use a Lothar Walther Barrel. I have not herd of them even working with this caliber any for data. Just asking?

 

[strictlyRUM]

Re: .338/408 CT & GSC bullet

I would like to try the Melanite coating with one of the 338/408s to really test the added barrel life.

 

[ARMECA]

Re: .338/408 CT & GSC bullet

Thanks to all for your answers, and to Noel for his aeroballistic lesson.

If I undertand correctly, it will be better to keep the .338 - 7" LGT barrel for a .338 LM and shoot the GSC 267 grs bullets ( or equivalent ), and keep the CT action for a .375 CT with a 8" exit twist barrel ?

Thanks again !

PS : Noel, can you send your bullets to France ?

 

[ARMECA]

Re: .338/408 CT & GSC bullet

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GLOWWORM</div><div class="ubbcode-body">Not meaning to start anything but why would you use such great components like the Barnard action and then use a Lothar Walther Barrel. I have not herd of them even working with this caliber any for data. Just asking? </div></div>

I know LW are not the best barrels in the world but they are not so bad ! Also, they are the only ones in Europe to offer LGT barrels. And they last for ever !

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Armeca,

A standard 1: 8" twist will stabilize the ZA375/6.0-M very nicely at all velocities. I assume this would also be true for the GS, or LM equivalents. You will be far ahead if you mount an LGT barrel however. One of the issues I had to address in the, soon-to-be-posted, bipod design was axial-torque. This issue is largely mitigated with a 2:1 LGT rifling geometry.

If you have the patience, a 375 LGT barrel produced in the U.S. is your best alternative, and the <span style="font-style: italic">only</span> option should you decide to use 6.5, or 7.0 caliber projectiles. The 338 LW-LGT you have on order is fine for banded-solids up to 6.0 calibers, assuming adequate projectile design proofing.

I am orchestrating the completion of a number of projects in coordination with each other. Projectiles will be publicly available soon, and exportation to Europe is a part of that plan.

Best,
Noel

 

[strictlyRUM]

Re: .338/408 CT & GSC bullet

Hey Noel,

Have you tried or have known anyone that has tried the melanite coating on these big boomers? I would like to know what it would do. It would make it easier to spend the money on componants if I knew I was going to get more than 800 rounds out of a barrel. Thanks

Jason

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Hello Jason,

I know very little about melanite, but I am curious. I did my best to gather information on this material in a gun-bore application, and could find precious little.

Obviously, that is not a measure of efficacy, but it does raise a red flag.

You are absolutely right about the throat-life concern. I have a proven solution, but it requires a special shell case to dispense the ceramic protectant. This is one of the many projects I am attempting to time with the public release of the ZA projectile.

Best,
Noel

 

[C.K]

Re: .338/408 CT & GSC bullet

Noel, get a hold of Mike Wright of H.E.F. USA, (937) 323-2556. If you want to talk Melonite coatings.

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Thanks CK

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Chad,

I just looked at the H.E.F. website, with a cross reference to Mike. "Melonite" is nothing more than carbonitriding.

For resistance to heat erosion, it is useless. For reduction of friction, and mechanical wear resistance, it is great... good process, bad application.

Best,
Noel

 

[BLAWTON]

Re: .338/408 CT & GSC bullet

Nitriding maybe? Noel give me a call and i might be able to get you in touch with a few people that could help.

 

[BLAWTON]

Re: .338/408 CT & GSC bullet

I have talk to a few people that have done melonite in the past and with very little success. It was causing excessive cracking and chipping in the bore. I will have to do some more research and find out whats so different about the new processes that will help with this problem.

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Shallower carbon, and/or nitrogen, penetration will help with the "checking" effect. I am extremely skeptical of the proposition that any heat-erosion resistance benefit is conferred.

In discussing the process with the sources you gave me Bobby, their take was essentially the same.

If someone has some direct experience to the contrary, I am very interested in hearing from you.

Best,
Noel

 

[Gerard Schultz]

Re: .338/408 CT & GSC bullet

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The GS is essentially a tangent ogive</div></div> Definitely not a tangent ogive. An easy 2850FPS from a 28" barrel in a Lapua Magnum and, if memory serves, Tom Marsti used a LW barrel to shoot highest score four times in a row at the Lapua / Finn Sniper with his TRG in 338 Lapua Magnum.

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Hello Gerard,

You are using a single radius on the nose, correct?

The bullet used by Marsti is different in all respects from the sample which I have of your 338. I have the projectiles to compare side by side, and it is much closer, especially in tail configuration, to the LM-119, and Viking.

 

[Gerard Schultz]

Re: .338/408 CT & GSC bullet

Hi Noel,
GSC did the original prototypes of the bullet used by Marsti. The bullets he actually used were manufactured by KJG and were identical. The reason given by KJG why they supplied the bullets, was ostensibly that we could not produce them at the time. Fact is we did not get an order to supply.

The 295gr 338 SP we currently make, is a third generation improvement of the original prototype. That is probably what you have.

I mentioned Marsti not because of the bullets he used, but because he used a Sako TRG fitted with a Walther barrel.

 

[Noel Carlson]

Re: .338/408 CT & GSC bullet

Gerard,

Good to hear from you.

Yes, I am sure the sample which I have is your most current version. We need to discuss some things, but I believe it would be best to communicate off-line.

Watch for a PM.

Best,
Noel