1-8 or 1-7.5 twist for 6.5 CM

[parkerg31]

Looking to put a new barrel on my 6.5. Can anyone fill me in on the differences and advantages of a 1-7.5 twist or a 1-8 twist over the other.

 

[Sniper266]

Generally speaking: a faster twist can better stabilize a heavier bullet.
However there is a school of thought that you can over stabilize a lighter bullet.
So the real question is what bullet do you plan to shoot at what velocity?

Once you know this you can us bergers stability calculator and find out what twist rate is best. You want your stabilization number to be between 1.5 and 2, but not over 2 if you believe in over stabilization. The closer to 2 the better because as velocity drops over distance so will the stability number and thus you are “less stable”

 

[AIAW]

Looking to put a new barrel on my 6.5. Can anyone fill me in on the differences and advantages of a 1-7.5 twist or a 1-8 twist over the other.

1.625 MS with a 1-8" vs 1.849 MS with a 1-7.5" - 147g ELD-M.

If you shoot heavier bullets out the 6.5 then it might be slightly beneficial. Anything below a 140g though the benefit is null.

The being said, I have zero complaints out of my 1-8"'s. I run 140g's primarily - Gives me no reason to specifically spec a 1-7.5" in the future really.

 

[Sniper266]

Below are some numbers that i quickly pulled togther that may or maynot directly apply to you, but can be used as reference to better illustrate the difference in twist and its affect on stability. I belive on the berger calculator it says that anything between 1.0 and 1.5 is “marginally stable and you may get good groups”.

120 eldm
-.486 BC
-22” barrel
-2900fps
-bullet length 1.202”
-1-8 twist Stability number is 2.18
-1-7.5 twist stability number is 2.48

140 eldm
-.646 bc
-22” barrel
-2805fps
-bullet length 1.3785”
-1-8 twist stability number is 1.69
-1-7.5 twist stability number is 1.92

 

[VegasHKShooter]

Agree with the 1/8. I shoot Hornady 140 ELD-M, Hornady 143 ELD-X, and 147 ELD-M. I have never had a stability issue out past 1200-1300 yds.
I shoot 140 most due to the fact that they do fantastic in my gas gun and my bolt gun. I only have to keep one type bullet around instead of “gas gun” rounds and “bolt gun” rounds.

BTW, the 143 ELD-X shoot fantastically accurate. If you hunt at all give them a look. If that was the only 6.5CM I could shoot, I wouldn’t be mad.

 

[AIAW]

Yep, same here. Short of running heavy VLD’s in a long-throated chamber, I feel the 1-7.5” isn’t warranted.

 

[XLR308]

I went with a Bartlien 7.5 twist for my first and only 6.5 Creedmoor but my main interest was from the start to run the 147eldm and 150smk.
The 7.5 twist should be no disadvantage if I decide to run bullets in the 130 class down the road but I have a 6.5x47 I'm working on now for running the lighter bullets in a lighter rifle for hunting so I'm covered either way.

 

[GIXXER2000]

I went all out and had a 1-7 Twist 26 in Bartlien for both the 6 and 6.5 CM. Plan on shooting the 150 SMK or 147 ELD-X in the 6.5cm and 110 SMK or the 115 DTAC in the 6cm. I am working on a barrel change today so hope to have that completed later today and start working up a load for both.

 

[Rob01]

Unless you plan to shoot heavier than 147s then the 8 twist will be fine. Up to and including 147s will be fine in an 8 twist.