Which chamber for a custom bolt gun?

[Drifter]

But that's not an actual 6.5 Grendel chamber. That's why I asked the original question... Which "non-Grendel" chamber is best for a bolt gun?

There are a ton of people out there building barrels that will work with 6.5 Grendel ammo, but I'm looking for the best, most accurate one.

All other barrel aspects being equal, the CSS chamber should be equal to or better than the Grendel in terms of accuracy. I think the primary difference between the two is the tighter neck of the CSS. I believe both have compound-angle throats.

As for pre-fit options, the CSS might be the only one. Obviously, a custom job expands the options, but also the cost and time frame.