Never had a bore scope ... but my guess... as the bullet moves forward in the bore, it pushes the bulk of any oil present ahead of it, resulting in a buildup which results in increased pressure. There would be very little lube left to adhere to the bore towards the shank end of the bullet so the jacket would start to shed copper. It would be logical to assume more copper would be shed in a “rough” bore.
Now, back to the effect on the “wet” shot which may have a different POI down range due to a different velocity related to the pressure buildup. It follows that subsequent “dry” shots would be relatively consistent, at least until the buildup of copper results in change. Copper adheres to copper more than copper adheres to steel ... but that is another issue.
Well, right or wrong, that’s my theory
