Did some research, last thread I saw arfcom was 2015.

Any reason NOT to get 7.5 instead of 8?

Velocity may be less, but I plan a long (29") barrel so I think I'd still have similar/better velocity than someone with an 8 twist shorter barrel (?).

I used the Berger stability calculator and ran pretty much all of their bullets from 130 up with various speeds and all stable in the 7.5 (and stability for all slightly better than the 8 twist).

Bench shooting for groups.
MOSTLY 200yds but can drive 1.5 hour for 3/800 yd range.  

I'd like the ability to use the VLD type and heavy bullets even if it isn't what I load up for my routine (200y) shooting.

Anything 1:8 does that 1:7.5 can't?

ETA: New to bolts, new to 6.5CM so no idea what bullet will wind up being best for me/my rifle.
Will hand load for it, probably factory loads at first to get a feel for it and what it likes.
Did get a Wyatt internal magazine so I have option of mag loading longer OAL and will single feed if that's what it takes, so not concerned with OAL.

6.5 Creedmoor, plan Bartlein heavy varmint barrel 29"

Thanks.
I'm building.
Southern Precision/Bughole is where I plan to get the barrel and have do the chamber/finish work.

Just talk to Greg or Russ at SPR and tell them what you are doing. They will be happy to make a recommendation on both chamber and recommended twist along with the plus and minuses of what you are trying to do.
They've done three (3) 6XC barrels and one (1) 308 for me and I am thoroughly satisfied with results.

Your twist rate selection will have virtually zero effect on velocity. Too many other factors will contribute to higher/lower velocity from any given barrel to worry about that.

this



those guys do good work just take their recommendation

As has been stated the formula is already figured out.

1:8 twist with a .199 freebore is what you want. It will shoot everything factory, and will shoot all but the heaviest (and not ideal for the CMs lower powder capacity) 6.5 bullets.

Don't over think this.

Thanks all!