Muley. I have tried 2 different brands of barrel, both good brands, but have had one rechambered 3 times. It was first in a Panda, then a Barnard, then rechambered for the Panda again,2 different gunsmiths, 2 reamers, 3 chambers, the last reamer .002 wider, with a slightly longer throat.
I have had the older barrel go very very well for a while, then next time I use it in a big comp, it plays up again, nothing realy realy bad, but definitley makes Xs a hit and miss affair. I monitor the velocity and keep the same powder lot numbers, same bullet lots, but still got what a few shooters here in Australia call 6x47itis. My latest barrel is currently going very well, after taking 300 rounds to get it working well. Groups hovered around 1 moa with 3 different powders, 4 different bullets, but is now MUCH better than this in a narrow seating depth and powder weight window. I still want to use it for a few more shoots before I use it in a big comp.
As you say though, this is a limited sample and one of the most accurate guns I have seen lately was a 6x47 through 3 days of competition.
A few other shooters in my area have had a similar experience, different reamer than mine, different barrels, but found it more finicky with tuning and keeping in tune than a Dasher or BRX. These are shooters who have won big competitions and have shown they can get rifles shooting well. A C grader might be happy with the accuraccy, but A graders are after more consistancy.