6.5 Creedmoor 1/7 Twist barrel

[00bullitt]

I'm curious to get the thoughts of those on here about my next rebarrel. I've shot my 243 out at 1400 rounds and have decided to give the 6.5 Creedmoor a shot.

I am of the belief that in a shorter barrel a faster twist rate for moderate velocity cartridges will provide better accuracy through better stabilization at longer ranges.

My goal for twist rate is to usually see that a bullet will get 3 full rotations prior to exiting the barrel. That is why I came up with 1/7 twist.

My intent is to rebarrel with a 22" Bartlein in 1/7 twist and shoot 142 SMK's. Why 22"? I wanted my bolt gun to match my gas gun length and the 1/7 twist met my criteria for 3 revolutions prior to exiting the muzzle. 1/7 is not an available twist for 6.5 but Bartlein did one for the additional tooling cost.

I've witnessed 12.5" 308 bolt guns shooting 1/6.5 and 1/7 twist barrels shoot 175 SMK's sub MOA at 1k while a 12.5" 1/10 couldn't do 3 MOA at 1k. My thoughts were that there was something to that. Ever since Norm Chandler explored accuracy potential of shorter barreled 308's such as the XM3 and found the 1/10 superior for accuracy at extended ranges, I have been intrigued to try something similar.

I tend to believe that low to moderate velocity cartidges can benefit from faster twist barrels for LR performance. I'm not concerned as much with accuracy at 100 as I am 200 and beyond.
Although the 12.5" gun I witnessed would shoot 3/4" at 100 which is totally acceptable assuming my LR Performance was improved.

What are the thoughts of those on here? Is my thought process sound?

 

[turbo54]

I had a 22" 260 with a 1:8.5 Bartlein that would hammer the 140gr bullets at 100, 500 or 1000 yards.

If it's an idea that intrigues you, go for it.

Let us know what you learn.

 

[peaceatwar]

I'm curious to get the thoughts of those on here about my next rebarrel. I've shot my 243 out at 1400 rounds and have decided to give the 6.5 Creedmoor a shot.

I am of the belief that in a shorter barrel a faster twist rate for moderate velocity cartridges will provide better accuracy through better stabilization at longer ranges.

My goal for twist rate is to usually see that a bullet will get 3 full rotations prior to exiting the barrel. That is why I came up with 1/7 twist.

My intent is to rebarrel with a 22" Bartlein in 1/7 twist and shoot 142 SMK's. Why 22"? I wanted my bolt gun to match my gas gun length and the 1/7 twist met my criteria for 3 revolutions prior to exiting the muzzle. 1/7 is not an available twist for 6.5 but Bartlein did one for the additional tooling cost.

I've witnessed 12.5" 308 bolt guns shooting 1/6.5 and 1/7 twist barrels shoot 175 SMK's sub MOA at 1k while a 12.5" 1/10 couldn't do 3 MOA at 1k. My thoughts were that there was something to that. Ever since Norm Chandler explored accuracy potential of shorter barreled 308's such as the XM3 and found the 1/10 superior for accuracy at extended ranges, I have been intrigued to try something similar.

I tend to believe that low to moderate velocity cartidges can benefit from faster twist barrels for LR performance. I'm not concerned as much with accuracy at 100 as I am 200 and beyond.
Although the 12.5" gun I witnessed would shoot 3/4" at 100 which is totally acceptable assuming my LR Performance was improved.

What are the thoughts of those on here? Is my thought process sound?

There is some definite sound logic in here.

Estimating that you can push them 2700 fps(which seems moderate for a 22" with a 142 SMK to me)

Yardage / Drop in Mils / 10 MPH Wind in Mils. My quick JBM shows that load going transonic around 1400. (550 ft Altitude, 80 Degrees F, 64% Humidity)

(yd) (mil) (mil)
100 0 0.2
200 -0.6 0.3
300 -1.4 0.5
400 -2.2 0.7
500 -3.2 0.9
600 -4.2 1.1
700 -5.3 1.3
800 -6.6 1.6
900 -8 1.9
1000 -9.5 2.1
1100 -11.2 2.4
1200 -13.1 2.7
1300 -15.2 3.1
1400 -17.5 3.4

9.5 Mils of drop @ 1000 with 2.1 Mils of wind isn't bad. You are getting a softer recoiling but compareble ballistics to a hot-loaded .308. As for the twist/stablization I see no reason not to go with 1/7 if you are sold on the heavier bullets. I'd be interested to see how the 139 or new 136 Lapua Scenar would perform in that platform. I have a 6.5 Bartlein MTU 1:8 blank I have sitting in the safe for my own project like this. Planning on finishing mine at 24" though.

 

[00bullitt]

I know for a fact that a 1/8 - 1/9 will hammer the 140's and 142's. The 1/8 seems to be the norm for most shooting the heavier pills, mostly in 24-26" barrels.

I wanted to try a 1/6.5 in a 20" but I think I will start with a 1/7 in a 22" since my JP gasser is 22". I can keep similar ballistics memorized in my head easier.

If this works out as I hope; maybe next I will do a 20" 1/6.5 in my JP.

 

[peaceatwar]

I know for a fact that a 1/8 - 1/9 will hammer the 140's and 142's. The 1/8 seems to be the norm for most shooting the heavier pills, mostly in 24-26" barrels.

I wanted to try a 1/6.5 in a 20" but I think I will start with a 1/7 in a 22" since my JP gasser is 22". I can keep similar ballistics memorized in my head easier.

If this works out as I hope; maybe next I will do a 20" 1/6.5 in my JP.

You ever thought of a hybrid progressive gain twist?

 

[R6Hybridd]

You ever thought of a hybrid progressive gain twist?

Can someone explain the benefits of progressive rifling. I understand how it works but what is the benefit of starting at say a 1:11 twist and ending at 1:8, the bullet would still leave the barrel at a 1:8 twist. I'm not saying there s no benefit, I'm just looking for education.

 

[KYS]

You ever thought of a hybrid progressive gain twist?

There is really no point in running a gain twist on a 6.5 Creedmoor. I've had the bust luck with 1/8.7
The gain twist barrels really shine on 260's and 6mm Creedmoor. Not saying you can't use them but there is no need.

 

[turbo54]

Can someone explain the benefits of progressive rifling. I understand how it works but what is the benefit of starting at say a 1:11 twist and ending at 1:8, the bullet would still leave the barrel at a 1:8 twist. I'm not saying there s no benefit, I'm just looking for education.

The concept is the bullet doesn't have to go from zero rpm to 200,000rpm instantly. That is better because.....it just is.

How is a rainbow made?

Why is the sky blue?

Hows the posi in a plymouth work?

It just DOES!

 

[turbo54]

There is really no point in running a gain twist on a 6.5 Creedmoor. I've had the bust luck with 1/8.7
The gain twist barrels really shine on 260's and 6mm Creedmoor. Not saying you can't use them but there is no need.

Would love for you to articulate to us why gain twist is good/useful in 260 and pointless in a 6.5CM...

 

[KYS]

Would love for you to articulate to us why gain twist is good/useful in 260 and pointless in a 6.5CM...

Because I trust what my rifle builder and ammo company tells me. I was wanting to use my gain twist stash of barrels for a 6.5 Creedmoor and was advised there was no advantage in accuracy only a SLIGHT speed gain.
The 6.5 CM is a touch more efficient on its case design and burn rate so you can get it going faster with less pressure then a 260. So if you want to push it..... use the gain twist. If you want a 260 to catch up to what a 6.5CM can do, go gain twist.

I just don't see the point in using a barrel twist that give you a few fps advantage when you can go traditional rifling and save a few dollars on barrel cost. Just my opinion on it.

 

[bbcellars]

Can someone explain the benefits of progressive rifling. I understand how it works but what is the benefit of starting at say a 1:11 twist and ending at 1:8, the bullet would still leave the barrel at a 1:8 twist. I'm not saying there s no benefit, I'm just looking for education.

I was told by a gentleman at Bartlein that they've had the best luck with progressive twists that only get tighter by 1 inch or less...for example, 1:11 to 1:10 twist, and that was on a 26" - 28" barrel. I told him my finished length would be 24"-26", and he suggested going with only a .75" decrease. These were for a 6 creedmoor and 7Saum, so not 100% sure on a 6.5, but I'm guessing...

Hope that helps...

I love my gain twist 243 BTW...Bartlein finished at 28" with a 1:8.5-1:7.5....

 

[Rockfish Dave]

All mine are gain twist barrels. Honestly, I doubt many here are good enough shooters to benefit from any incremental benefit since the non-gain rifle barrels shoot so good anyways.

So why did I get the gain twist? Honestly, just because I can.

 

[gugubica]

I am getting over 2800 fps from factory 140gn. Rock 8 twist 5R finished at 22.75...yes, i am very happy with these numbers.

try it, ya never know. In reality, you would have to get real lucky to wind up with the same velocity, without tuning your load for each, from your bolt and gasser, same barrel length or not...just to many variables.

 

[Sonic Crack]

I've witnessed 12.5" 308 bolt guns shooting 1/6.5 and 1/7 twist barrels shoot 175 SMK's sub MOA at 1k while a 12.5" 1/10 couldn't do 3 MOA at 1k. My thoughts were that there was something to that.

While I think there is some merit to the twist, I know there is a LOT more to it than that esp at 1k. I'd say go with any 8 twist and forget about it. Put all that energy into practicing the fundamentals, that will get you more accuracy than the difference between 7 and 8 twist at any range.

 

[VKC]

A faster twist barrel in theory will give your bullet more stability as it transitions to subsonic velocity. However you can suffer some accuracy loss at closer ranges depending on how fast of a twist.

JBM - Calculations - Stability

Use the Miller stability formula and plug in some numbers to see what you need.

For a 6.5 Creedmoor it isn't going to go subsonic until way beyond 1000 yds.

For my rifle, in my shooting conditions, my calculations show that pointed 142smk don't go subsonic until around 1800yds. With wind drift and bullet mass, I don't think that there are many shooters that could call wind that precisely or spot their bullet splash at that distance. Of course it will depend on the target size, but that is just me.

I will post a link that I started which explain these thoughts in further detail.

 

[VKC]

http://www.snipershide.com/shooting...50-1420-yds-my-limitations-6-5-creedmoor.html

 

[lifebreath]

My 6.5 is 1 in 8, 26". I can see tightening up a little in a short barrel, and a progressive twist would interest me. Why? Because my background is in mathematics and it just seems cool! Plus, the rate of twist is increasing, so it will impart a rotational acceleration to the bullet. Without really thinking through it, my initial thought is that you can achieve the equivalent of a higher twist without actually having that twist. For example, if you start at 1:8.5 and progressively increase the twist to 1:8, the bullet will have a slight rotational acceleration and the resulting peak rotation of the bullet will be greater at some point after leaving the barrel and will be greater than if the twist was a constant 1:8.

In short, it just seems cool. ;-)

 

[creedmoor664]

I was told by a gentleman at Bartlein that they've had the best luck with progressive twists that only get tighter by 1 inch or less...for example, 1:11 to 1:10 twist, and that was on a 26" - 28" barrel. I told him my finished length would be 24"-26", and he suggested going with only a .75" decrease. These were for a 6 creedmoor and 7Saum, so not 100% sure on a 6.5, but I'm guessing...

Hope that helps...

I love my gain twist 243 BTW...Bartlein finished at 28" with a 1:8.5-1:7.5....

I can tell you that my new Bartlein 9-8 twist 6.5 CM barrel on my RPR took me from 1/2 moa to 5 shot groups without paper between in a 1/4" Of course that was comparing a factory RPR barrel to the new Bartlein twist barrel. I did the 1" gain twist as recommended by Tracy.

 

[RushT]

My 6.5 is 1 in 8, 26". I can see tightening up a little in a short barrel, and a progressive twist would interest me. Why? Because my background is in mathematics and it just seems cool! Plus, the rate of twist is increasing, so it will impart a rotational acceleration to the bullet. Without really thinking through it, my initial thought is that you can achieve the equivalent of a higher twist without actually having that twist. For example, if you start at 1:8.5 and progressively increase the twist to 1:8, the bullet will have a slight rotational acceleration and the resulting peak rotation of the bullet will be greater at some point after leaving the barrel and will be greater than if the twist was a constant 1:8.

In short, it just seems cool. ;-)

Bit of an old post here, but I’m not sure about the peak rotational velocity occurring after leaving the barrel. At the moment of exit, there’s a specific rotational rate. At that same moment, you lose all torque on the bullet, so that rotational rate is probably fixed at that point. I‘m just beginning my long range journey, so perhaps there’s some subtlety I’m missing.