OzFclass

for many barrels clean to dirty was very predictable.
shot 1, 1 to 2 minutes low.
shot 2 about 1/2 moa low.
then stedy as you go.
you got used to that barrel and acted accordingly, such that it did not realy matter if you had no blowoff shots.
a barrel i have now shoots the 1st 4 or 5 the same, and then suddenly jumps to the high 5 ring.
this in itself, while a pain, could be managed, but it is not always the same shot no.
did i run in the barrel too much or not enough?
could there be a problem with chambering?
am i cleaning too much or not enough?
freebore diemeter/clearance too much/too little?
other?
keep safe,
bruce.

I would say not enough cleaning (but it may just be the very last step). At our club we did a little study on this and found some time ago that the first shot or two was slower causing this (30-60 fps). We then had some members with new barrels and again right from the start we put them over the chrono and with a clean dry "dry" being very important ie cleaned with a carby or brake cleaner and dry patched to remove any traces of oils that the first shot was the same as the tenth and no indication of any movement was on the target. From that those with newish barrels gave them a proper scrubbing and the same before shooting treatment and very similar results were obtained the first to 3rd speed differences where greatly reduced if not entirely.

Is there an associated FPS jump or POI is now suddenly higher but nothing else obvious? Does it stay settled after that or do you "chase it" a bit?

Not a scope issue? I had a similar experience and found its the scope that has an issue, no problem on smaller adjustments but when going from 300 yard setting to say 600-700 yard settings it wouldn’t actually move the full amount. You would then adjust to correct and on the fourth or fifth shot it would finally move requiring readjustment, usually back to near the first adjustment. Was unpredictable and could happen between shot 3and 6.