8.5 twist questions

[CM21VE]

I am going to purchase another kreiger BBL for. 6.5x47L, my question is, will this stabilize Lapua 136-139 scenars? Ive had both 8 and 8.5 twist but never tried anything bigger than a 130 vld out of the 8.5.
What about a 140hybrid?
Any input would help.

Much appreciated

 

[JRS]

For the 140, Berger suggests the 8 twist.

Edit: After looking at the Berger website, they suggest the 8 twist for their 130-140 grain bullets.

 

[ShootDots]

I have a 6.5 x 47 at this time. It has a 30" 1-8.5 twist barrel. I am shooting the 136 Scenars and at 300 yards they are basically shooting under 1" at 300 yards. It is travelling at 2835 f.p.s. So, to answer your question, it will stabilize the 136's and the difference between them and the 139's is so small, I believe it will shoot those fine too..

 

[LarryDScott]

If you choose a border line twist rate, you groups
can go south on you, in drastic temperature changes.
I saw this in a friends 6.5-284. LDS

 

[RonAKA]

I am going to purchase another kreiger BBL for. 6.5x47L, my question is, will this stabilize Lapua 136-139 scenars? Ive had both 8 and 8.5 twist but never tried anything bigger than a 130 vld out of the 8.5.
What about a 140hybrid?
Any input would help.

Much appreciated

Berger generally recommends the next fastest round number twist, to be conservative. You need to use their twist rate calculator to be more accurate. Most important enter your elevation. Temperature and velocity are less important, but enter them too. For Berger bullets most can be entered from their lookup. For other bullets you need to get bullet length elsewhere. And you need the BC from Lapua for their bullets. For the 139 Scenar I get 1.364" for length, and 0.290 for G7 BC. At sea level and standard temp this gives a good Stability factor of 1.53, so you are fine with a 8.5 twist. The Berger 140 Hybrid comes out at 1.4 at sea level, meaning you compromise BC by 3%, but the bullet is still stable. At 2000 feet stability is 1.5 and no compromise to BC. Some links below.

Bullet Length Database

Lapua Scenar Bullets

Berger Twist Rate Calculator

And, I sure hope 8.5 is OK as I have one on order. I shoot at 2000+ feet so I'm sure it will be good. And if you compromise accuracy does not go off the cliff. Just your BC is reduced.

 

[mikegaiz]

1 in 8 works well for me, see attached article.

http://bulletin.accurateshooter.com/2016/08/amazing-2-856-10-shot-group-at-1000-yards/

I never got 120s or 130s to shoot well in this twist,

 

[CM21VE]

Berger generally recommends the next fastest round number twist, to be conservative. You need to use their twist rate calculator to be more accurate. Most important enter your elevation. Temperature and velocity are less important, but enter them too. For Berger bullets most can be entered from their lookup. For other bullets you need to get bullet length elsewhere. And you need the BC from Lapua for their bullets. For the 139 Scenar I get 1.364" for length, and 0.290 for G7 BC. At sea level and standard temp this gives a good Stability factor of 1.53, so you are fine with a 8.5 twist. The Berger 140 Hybrid comes out at 1.4 at sea level, meaning you compromise BC by 3%, but the bullet is still stable. At 2000 feet stability is 1.5 and no compromise to BC. Some links below.

Bullet Length Database

Lapua Scenar Bullets

Berger Twist Rate Calculator

And, I sure hope 8.5 is OK as I have one on order. I shoot at 2000+ feet so I'm sure it will be good. And if you compromise accuracy does not go off the cliff. Just your BC is reduced.

Thank you for the reply. Much appreciated. I will probably just try the scenars and stay away from the hybrid....

 

[CM21VE]

1 in 8 works well for me, see attached article.

http://bulletin.accurateshooter.com/2016/08/amazing-2-856-10-shot-group-at-1000-yards/

I never got 120s or 130s to shoot well in this twist,

Yeah i seen this, problem is that since you shot this ridiculously unbelievable group the 6.5 HV 31" kreiger 8 twist 4 groove have been flying off the shelf! Takes alot of time and effort to shoot like that, Great shooting there sir. Congratulations are well deserved.

 

[mikegaiz]

I have shot VLDs and Hybrid 140s they shoot well in 1 in 8. same with 142 SMK.

 

[CM21VE]

Kreiger actually just called me back and told me they have a 8 twist in stock and would re-contour it to what i wanted, good now i dont have to worry about it! I absolutely appreciate the replies from everyone!

 

[Fulvio]

I am shooting the 140 Hybrid in a 30" 1:8.5" barrel without any problem of stability. I shoot at sea level with temperature in the 80s. I point my bullets so even if a loose 1-2% of BC with a faster twist, this is more than compensated by the pointing.

 

[RonAKA]

I point my bullets so even if a loose 1-2% of BC with a faster twist, this is more than compensated by the pointing.

I believe it is slower twist that causes a loss in BC, not faster twist...

 

[loud_noise]

I have been watching this thread with great interest as I have been encountering real difficulties in getting 140gn Berger Hybrids to group properly out of a 22" 1-8 twist Tikka.
A lot of you guys are running longer barrels but would barrel length have a major impact on stabilising a round?

 

[Darrel Martin]

I have been watching this thread with great interest as I have been encountering real difficulties in getting 140gn Berger Hybrids to group properly out of a 22" 1-8 twist Tikka.
A lot of you guys are running longer barrels but would barrel length have a major impact on stabilising a round?

An 8 twist should have no problem stabilizing a 140 hybrid. Barrel length (ie velocity achieved) has much less effect on stability than twist rate.Higher velocity does increase the spin of the bullet , but that is offset somewhat by the fact that increased velocitry also increases the destabilizing force exerted on the nose of the bullet.

 

[hogpatrol]

I have an 8.5 brux #3 hunt on a trued 700 action and have shot the 130s, 140s and the Scenars with no issues. The scenars shoot the best but I don't use them for hunting. RL 17 for all weights.

 

[RonAKA]

I have been watching this thread with great interest as I have been encountering real difficulties in getting 140gn Berger Hybrids to group properly out of a 22" 1-8 twist Tikka.
A lot of you guys are running longer barrels but would barrel length have a major impact on stabilising a round?

Just put your muzzle velocity, temperature, twist rate, and altitude in the Berger twist rate calculator at the link below, and select the Berger bullets you want to check from the drop down list. Muzzle velocity has some effect, but altitude has more. Although the optimum twist stability is 1.5, accuracy does not suffer unless you go significantly below that. Your ballistic coefficient does suffer though. The Berger calculator will give you the details.

Berger Twist Rate Calculator

 

[okie]

date...

 

[wkdickinson]

Why limit yourself to what bullets may or may not work by being on the edge of stability (8.5" vs 8" or 7,5")? From what I have read, much of it by very credible people like Bryan Litz, the only downside of over stabilizing a bullet is the potential for shedding jackets. Which I doubt is an issue with a 6.5X47L.