While no 6CM, I have plenty of Berger in 6.5CM and 308 in a few different weights to compare to the rest of my lot (Federal GMM, Prime, Lapua).
The 6.5CM has been shot out of 3x different barrels as has the 308's.
In pretty much every case, the Berger is slower and prints bigger groups than the aforementioned ammo with similar or same projectile.
On top of that Molon's debacle with the .223 Berger in his semi auto has also not helped my confidence in them either.
In speaking with some other members they've noted Berger loaded ammo being touchy from rifle-to-rifle or barrel-to-barrel.
To put it simply, it's been very disappointing in my guns.
Still love me some Berger projectiles though...