as a newbie to 410 shooting I have much to learn. Recently I ran out of 8.5 shot so reloaded 8's. My 410 mentor and I were shooting together and I was really struggling on 1 particular bird. He asks me what i was shooting, so i responded 1/2 oz of 8's. What choke, I was using a gun I had acquired from him with .008 chokes. Without a pause he informs me when I went to 8's from 8.5 I was using 16% less shot, so needed tighter chokes to maintain enough pattern density. I have since gone back and shot that station with .012 choke and hit consistently. To hit these birds with 6's or 7 1/2 I would guess they were using something like .012 to .016
