Vol, didn't you mean to say that you keep missing with the right barrel?
If the right barrel's pattern is centered to the right, it may be that it will be regulated for a longer distance than 20 yards. It just may not have "gotten to the centerline" yet. Back up to 30, and 40 and see. Sometimes this is the case. With full choked barrels, it would be more useful for them to be regulated out closer to 40 than at 20, anyway.
I've got a double that I have got to move the center of the pattern over 8 inches as well. But, it's left barrel shoots 8 inches right of POA at 25 yards. IOW, it's already crossed the "centerline", and only gets worse at longer distances. I still kill a lot of doves with it, but know it is causing me some misses, and lots of non-centered hits.
SRH
