I have one rifle that shot the group above... I have to add, that is not the average, that is the best I have ever shot. Average at 600 really isnt that much larger, but larger. Group above is at 600 and is below 1/2 moa. Average is usually 3/4 moa at 600.
A good friend of mine has a Douglas barrel on his SPR. His has been shot MUCH less than mine.. he hardly shoots it at all. I shoot it most often. It shoots pretty close to what my kreiger does, but I'd really want to shoot it more to gove a good comparison between the two.
I was just shooting the Douglas barrel gun today and it was doing really well with the 77gr Black Hills white box ammo and 69gr Fed Gold Medal, but I was only shooting at 100 yards.
Most any of the high end custom barrels you can get will probably shoot amazingly well if the gun built around it is as top shelf as the barrel. Ammo too. But I tell you what, its easy to throw money at a gun to make it shoot better... Belive me I've done that! In the end, the guns biggest shortcoming to the accuracy it can achieve is going to be its operator!