ORIGINAL: cayugad
What I do is learn where the rifle will shoot on a clean barrel, if I decide to hunt that way. Today I hunted a clean barrel and I know the rifle will shoot about an inch low. Well an inch at 50 yards means nothing to me. I aim dead center kill zone and let fly.
Bingo
In terms of all my rifles I want to know where they will shoot clean vs fouled. In terms of a sub shooting ML I have always started out each morning with a clean barrel so I learn its traits and know what to expect. I have been lucky that most of my inlines shoot very close clean so like cayugad mentions the small variance is a non factor.
Are you making sure all the oil is out of your barrel prior to loading it clean??? Increase in pressure due to oil left in the bore often shows a higher POI.