I know all about reading and thinking about something else! I don't read much actually.
On group wondering, I did see it to a small degree but satisfied that the gun had settled, I ventured to zero the scope, moving the POI to the left. Well, the group moved to the left but also moved down! Anyway, I got it centered - that's when I shot the black spot out before the jamb then I took the scope of to test the reflex. After putting the scope back on the POI had moved to the opposite side so clearly the scope wasn't stable on its rail the first time. I'll monitor that one.
I can understand the POI drifting with open sights because of light conditions changing but not aperture sights. I was aware of cheek and hand pressure. The 510 is bedded between the fore-end and the rear of the action with the center screw holding pressure. I wonder whether the rest position would have an effect? Perhaps I should have the rest under the bedding point?