What is the best twist rate for the Grendel.

[6.5 mm Shoot]

Hi all.

I am looking at having a barrel built that is a light weight and 20" long. I am looking at what twist rate it should be.

My 16" Alexander Arms barrel has a 1 in 7.5 and it shoots great.

Shilen states that a 1 in 9 will take care of bullets up to 130 gr. The heaviest bullet I will use in the Grendel will be 130 gr.

So what is the big difference about?

Thanks for any information you can offer.

[VASCAR2]

Bill Alexander has posted here before that during AA extensive testing it showed shorter barrels shot better with tighter/faster twist hense the 1:7.5" twist on the 16" and shorter barrels. A lot of companies are selling 1:8 twist in 18-20 inch 6.5 Grendel barrels. I have a 16" and 20" 6.5 Grendels and both are 1:9. I have been completely satisfied with both barrels but I haven't shot any bullets heavier than 123 grains. My SIL has a Lothar Walther 6.5 Grendel with 22" barrel and 1:9 twist. His barrel has been very accurate with Hornady 129 grain SST hand loads.

If I were buying a new barrel in 6.5 Grendel I would opt for a faster twist if it was available. Everything I read recently indicates most cartridges do fine with a faster twist than has been generally used.

[PrecisionFirearms]

Hand down: 1-8 Twist from our sizable experience.

[Drillboss]

Hi all.

I am looking at having a barrel built that is a light weight and 20" long. I am looking at what twist rate it should be.

My 16" Alexander Arms barrel has a 1 in 7.5 and it shoots great.

Shilen states that a 1 in 9 will take care of bullets up to 130 gr. The heaviest bullet I will use in the Grendel will be 130 gr.

So what is the big difference about?

Thanks for any information you can offer.

In general, a tighter twist is required to stabilize heavier bullets. I believe it's more due to the length of the bearing surface than the weight itself. Berger has a handy calculator for necessary twist rates:

http://www.bergerbullets.com/twist-rate-calculator/

My 20" 1 in 9 won't stabilize a 140 gr bullet until I get up to maximum loads.

[LRRPF52]

Have you ever played with a gyroscope?

Imagine a gyroscope that is starting to enter its phase where its spin stability decays and it "comes apart" from spin stability.

The faster the gyroscope is spun and its ability to stay stable are very helpful for long range shooting.

For shorter distances, it doesn't matter much, as flight time is so short that you connect almost immediately.

When you start to get out into ~800yds and beyond, depending on the altitude, BC, and spin stability, things can stay nicely spun, or come apart.

A really good example of this is the .308 Winchester with a 168gr SMK from a 12" twist barrel. They come apart quickly around 800yds.

Spin it faster, and you can actually extend the spin stab range of that bullet, like with 10" twist.

1/8" is an easy default for 6.5 Grendel, and I will also say that my 16" 1/7.5" twist AA barrel really surprised me at 1200yds with factory 123gr AMAX. AA uses 1/7.5" on 18" and less, and 1/8.75" or 1/9" on 20-24".

MV has an influence on spin stab because the velocity increases the rpms of the projectile, hence the slightly looser twist for longer barrels.

[Rknuesel]

Sighted in at 200yds. Group on the plate is from 700yds.
Hogden BL-C(2) 30.0 g, Hornady 129g SST, CCI 450, Hornady brass.
1/2 MOA accuracy.
1:8 Twist

[ahillock]

1/8" is an easy default for 6.5 Grendel, and I will also say that my 16" 1/7.5" twist AA barrel really surprised me at 1200yds with factory 123gr AMAX. AA uses 1/7.5" on 18" and less, and 1/8.75" or 1/9" on 20-24".

Did I read that correctly that you took your 16" AA barrel out to 1200 yards? I know you are at elevation, but still. That is quite impressive.

[nimitzman]

well said

[nimitzman]

was wondering if anyone has explored the lighter bullet higher velocity slower twist theory here ala .22 250