Confusion on bullet spin and weights in lighter 6.5's

[Tesoro]

Okay I have a new 6.5cm hunting rifle made for the 120-130gr range with a 26in 1:9 barrel. All I have done so far is broke in the bbl to their instructions. Now its time to pick a bullet to start with.

The 1:8 guys say better to have a faster twist as it will also shoot the lighter weights very well as you really cant over spin those bullets.

The Lapua guys and many others who are in the know say for the 120-130g range 1:8.5 or 1:9 is ideally what you want. The bullet techs say the same.

Obviously HS knows their shit and chose the 1:9 for my rifle for a reason.

So under perfect 600 yd conditions what differences would one expect to see shooting a 1:9 over a 1:8 with a bullet in the 120gr range? accuracy? pressure/velocity?

 

[dkhunt14]

You can overspin them. In a gun that shoots them fast, you can make them blowup. In your particular gun, I don't think you will see much difference in a 8 or 9 twist. The only thing is with the 9, it will limit you to not using the heavier bullets. You might have slightly less pressure but not enough where you will really notice it. Matt

 

[Bart B.]

The best twist is the slowest that keeps the bullet stabilized all the way to the target in the coldest weather it's used in. Any faster will cause the unbalanced ones to jump off the bore axis too much as they exit.

JBM Ballistics' stability calculator can tell you the twist needed for your bullet that produces a 1.4 stability factor. That 1.4 value is typically best.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

 

[Tesoro]

I ran the JBM for the 123gr eld match 3000 fps:
8 twist = 2.62
9 twist = 2.07

And for the 123 sst:
8 twist = 2.02
9 twist = 1.6