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Topic: Best 6.5 twist? (Read 481 times) previous topic - next topic

Best 6.5 twist?

I am trying to chose a barrel manufacturer and twist for a new 6.5 CM build.  I hadn't thought a lot about twist for 6.5 in the past like I do for .223.  I shoot mostly 140-147 grain bullets, and that is a pretty static weight.  What is the best twist for that weight?  Since there is usually no choice but 8 for factory barrels I hadn't thought about it before.  Just looking for opinions and why.  I shoot long and short range mostly from a bench.

Re: Best 6.5 twist?

Reply #1
Desired twist rate is partially dependent on bullet BC, velocity, and weight ,as well as, atmospheric conditions (DA/altitude).  Berger has a calculator based on the Miller Twist Formula that is handy to use.

https://bergerbullets.com/twist-rate-calculator/

Re: Best 6.5 twist?

Reply #2
I like 1-8 for that weight.  I think it's the most popular twist for 6.5 CM.

Re: Best 6.5 twist?

Reply #3
The 1 in 8 twist is the gold standard and will stablize the bullets
you have mentioned just fine.
That why most 6.5 barrel come with a 1-8
The only reason to go with a 7.5 tw is if you run at sea level, run the longer
Sierra 150's or shoot in the cold alot.
The only reason to run a slower twist (1-9) is if your shooting a lighter weight bullet, 120g or less.
For varmint hunting

Re: Best 6.5 twist?

Reply #4
IMHO, 1:7.5 is splitting hairs, even for 150's and the ubiquitous 1:8 is all that's needed for any 6.5CM rifle.

Re: Best 6.5 twist?

Reply #5
Barrel lengths and the speeds you are pushing will be the
main factor for choosing your twist rate. An 8 twist covers
a wide range, but the range does start to narrow as the
bullets get heavier and longer.  My choice to build on a 7.5
twist gives me room to explore them longer and higher  BC
pills where my 24" 8 twist starts getting marginal at speeds
I plan to investigate.....I don't believe in a gold standard
until I find it myself..... ;)

Keeping my bad Kharma intact since 1952

Re: Best 6.5 twist?

Reply #6
I am trying to chose a barrel manufacturer and twist for a new 6.5 CM build.  I hadn't thought a lot about twist for 6.5 in the past like I do for .223.  I shoot mostly 140-147 grain bullets, and that is a pretty static weight.  What is the best twist for that weight?  Since there is usually no choice but 8 for factory barrels I hadn't thought about it before.  Just looking for opinions and why.  I shoot long and short range mostly from a bench.

Not sure what platform you plan on building off of but, Criterion
offers 8 and 7.5 twisters ready to spin on for the 6.5 Creedmoor.
Keeping my bad Kharma intact since 1952

Re: Best 6.5 twist?

Reply #7
Up to the 147 an 8 twist will work fine. If going for the heavier bullets then go with a 7.5.

Re: Best 6.5 twist?

Reply #8
Keep in mind that spin stability is related to velocity, and that a slower spin is more accurate as long as it flies straight.  A high velocity light weight bullet can be stabilized a low rpm.  You only need higher spin to stabilize long bullets as they slow down.  This is why 6ppc target barrels have like 13"-14" twist.  The slower twist still stabilizes the round and you eliminate imbalance wobble.  Many people make the mistake of getting the fastest twist thinking that faster is better, but actually the slowest twist that will stabilize your round to your longest distance is the best. 

In the 6.5 cm, the 147's seem to be fine with 8" out to 1100 yds for me.  If you were running Berger 130's or something like that, then 8.5" might even be better, especially if you were shooting mostly closer ranges where you would stay very fast.  A varmint only design might even spin slower with even lighter bullets.  Most barrel makers have chosen 8" twist, but that is because the main design of the 6.5 CM is long range with long heavy bullets in the 140gr size range.  This appears to be your goal also.

Re: Best 6.5 twist?

Reply #9
Mr Emary and Mr DeMille got it right im thinking...   im sure they had good reason to go with a 1 and 8 twist.. I would stick to the horse that brought us here.....
Grant

Re: Best 6.5 twist?

Reply #10
In the 6.5 cm, the 147's seem to be fine with 8" out to 1100 yds for me.  If you were running Berger 130's or something like that, then 8.5" might even be better, especially if you were shooting mostly closer ranges where you would stay very fast.  A varmint only design might even spin slower with even lighter bullets.  Most barrel makers have chosen 8" twist, but that is because the main design of the 6.5 CM is long range with long heavy bullets in the 140gr size range.  This appears to be your goal also.

The lighter bullets work just fine in the 8 twist also. 120 AMAX and ELDs run great in 8 twist and I know people shooting lighter with 8 also and it works.

Re: Best 6.5 twist?

Reply #11
Thanks guys.  I have decided to go with the 1:8.  The next big decision is the barrel.  Hard to get opinions on that since everyone seems to have their own favorites that are not all the same.  I'm just going to have to roll the dice on my best information.  I hope I' right.  If not, I have other actions.

Re: Best 6.5 twist?

Reply #12
Grizzly Industrial has Bartlein Barrels in #11 and 1.25" straight profiles on clearance right now. Both profiles are 1:8 twist, and use 5R rifling. You might want to look at what they have to offer.

www.grizzly.com

Re: Best 6.5 twist?

Reply #13
Seems to me that twist rate depends upon the intended use of the rifle. The 6.5 CM was pretty much designed around 140 - 143 bullets.

Remington originally used a 1 in 9" for the .260 REM, and for a number of years while it was available, the CZ 550s in 6.5 x 55mm had a 1 in 8.67" twist. There is a saying that you can't over-stabilize a bullet, but it does raise questions in terms of dwell time in the bore and pressure/velocity related issues. REM has since changed to a 1 in 8" twist for the .260 REM. Since they have added the 6.5 CM chambering, that kinda makes sense in terms of manufacturing costs. The current CZ 557s do not list rate of twist for the 6.5 x 55mm or the 6.5 CM. ;)

Re: Best 6.5 twist?

Reply #14

 There is a saying that you can't over-stabilize a bullet

To the abrupt point of coming apart in mid flight. We call it,
shooting butterflys.....
Keeping my bad Kharma intact since 1952