Gain twist for a .338LM

[ArcticFun]

This is more out of sheer curiosity than anything. I've been looking around and researching the theory behind a gain twist and how it increases the velocity of the bullet for longer as it travels down the bore by, for lack of a better term, crossthreading it and keeping pressure levels up. Now as I understand a gain twist, it gets faster the farther away from the action you get. So I guess the question is this: Who has done a gain twist barrel for the .338LM? Who made that barrel? What length with what velocity?

 

[strictlyRUM]

Re: Gain twist for a .338LM

You really only have two options. Bartlein and krieger. The final or end twist you want to be the twist rate to stabilize the bullet. 9.75 or close rot the lapua and 300 grain smk. Typically .5 or .75 is the typical gain you want to avoid tearing up the bullet too bad. The gain also helps accuracy from what I have seen. I think the more even pressure does a lot for stability of the bullet also.

Jason

 

[ArcticFun]

Re: Gain twist for a .338LM

How does the cross threading affect barrel life? Is this one of those things where you build the rifle to shoot a particular bullet versus being able to shoot a variety of 300gr bullets?

 

[strictlyRUM]

Re: Gain twist for a .338LM

If anything it helps life just a bit. Just because the bullet isn't slamming into the tighter twist. Barrel wear takes place in the throat area. Mostly from heat. Usually you can drop you powder charge some time even go to a slower (cooler) powder to make use id the down barrel pressure. This all helps throat life. And no its not bullet specific. Use any combo that will stabilize. The 6mms that I have done shot the 105 class up to the 115s very well.

Jason

 

[Jeffvn]

Re: Gain twist for a .338LM

If you want a significant gain in the twist, as in say a 12" twist at the breech and to say a 5.4" twist at the muzzle, for your .338LM Improved, then you have only one choice - Bartlein. I have heard that several other companies are doing limited twists, say less than 1.0 to 3/4" total in gain, but it is my understanding, after talking to nearly everyone of them on the phone, that only Bartlein is a doing a large gain. There are others with gain twist .375 barrels out there, and they also were produced by Bartlein, at least the ones that I know about.

I talked to BOTH Frank at Bartlein and Noel at some length before I ordered the 12" twist to a 5.4" twist for my .338LM Improved. This barrel was spec'ed specificaly to shoot Noel's ultra high BC banded solids. Length - it is going to finish at 32", not including the break. Expected velocity is in the 2,950-3,000 fps range for teh ultrahigh BC banded solids that Noel is developing.

The Barrel has been delivered to my smith, but I have not yet shot the rifle. I expect it shortly, as Manners just delivered the T2-A adjustable stock to my smith also...

I forgot to mention that i have NO EXPECTATION that a jacked bullet will survive being shot from this barrel at my expected velocities. Even so, I'll be testing the Sierra 300 grain and Lapua 300 grain 338s, just to see. I fully expect the 5.4 twist to tear the jackets to shreds... It will be interesting to see what happens.

JeffVN

 

[ArcticFun]

Re: Gain twist for a .338LM

Hmm I will have to wait and read what your reveiw of that will be. IF I did decide to build a .338LM it would be just the Lapua because I don't want to fireform but I would have to do a small gain becuase I would like to run jacketed bullets.

Thanks for the info strictlyRUM sounds like a gain twist barrel the new 'black' if you get my meaning. Interesting to see how a 10" to a 9.5" with a 27" barrel shoots.

 

[bsalbrig]

Re: Gain twist for a .338LM

With these changing twist riflings, wouldn't a bullet be initially formed to whatever twist was starting out and continuously formed to the final twist. Could the continuous forming of the bullet be worse than all at once when the bullet slams into a normal barrels rifling.

 

[azsugarbear]

Re: Gain twist for a .338LM

I have a 270 Win. built on a mauser 98 action with a custom 26" barrel that starts with 1 in 14 and ends with a 1 in 10 twist at the muzzle. The technology has been around for quite some time now. This rifle has always been accurate, but I haven't been able to tell much difference between this one and some of my other standard twist barrels.

By the way, this rifle was built in 1962 by the same gunsmith that built Jack O'Conner's .270. What goes around....comes back around.

 

[strictlyRUM]

Re: Gain twist for a .338LM

Yes it is old technology. It is mainly used in shortrange benchrest. It has been resurging lately. Also the large gains are going to be more suited for bore rider banded solids. By the tight gain you will actually be loosing a large amount of your bands. If you can keep something there as far as the driving bands are concerned to keep a barrier for the gasses. I don't know but I would think less band surface would equal less drag?

Jason

 

[Jeffvn]

Re: Gain twist for a .338LM

Jason

I don't know what the resulting effects on the bands will be, but will know a lot more when i dig a few out of the berm at my range. A couple reasons for the gain are to ease the bullet into the extremely tight twists needed for final stability of this ultra high BC and ultr long bullet (in my case the 5.4" at muzzle) in a way that reduces initial chamber pressures, yes gain twist will consume the bands, but not competely so the gas seal in the barrel is maintained, and from what I am being told, there is a reduced (different) recoil impulse on the shooter. The last one is most intriguing to me, and we'll see, as I have a 9.3" straight twist 338 LM Improved also being built.