I will not go to a match or go hunting with out fouling the bore with 2 shots regardless of which rifle I am shooting a match or hunting with. I am not going to leave something to chance that I can take out of the equation. I trust the third shot out a barrel. Thirty years of past experience has taught me that. S1....you hit the nail on the head with trusting the third shot for predicability. I have shot my 300 WSM
and my 260 enough to know that around the 10th to the 13 shot with the both rifles I better take .25 MOA out of the scope or I am going to see one go high that will go into the 9 ring. And it does seem to depend to some degree on temperature as too just when the POI changes.
I have found this topic most interesting. I just picked up my new 260 yesterday evening from the smith. I spent a little while today starting to break the barrel in. Remembering this topic I shot one and cleaned for 10 rounds without a sight adjustment just to see if the rifle would show if it put the first shot from a clean bore in the same POI consistently. The 10 shots measured 1.29" so at least it seems consistent with a clean cold bore. I have no idea where the second shot will go. Tomorrow I will know where the second and third shot go as the break in is showing good progress I will shoot some three shot groups with the break in load. I don't expect great accuracy with the break in load as it is the 85 grain Sierra in an 8 twist barrel. I use the cheapest bullet I can find to do initial break in. That bullet didn't do very well accuracy wise in my other 260, but it loves the 142 MK. Will be interesting to see what happens tomorrow when I move to three shot groups.